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[PATCH 00/17] perf tools: Support overwritable ring buffer

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  [PATCH 00/17] perf tools: Support overwritable ring buffer Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 15/17] perf record: Read from backward ring buffer Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 01/17] perf tools: Extract __perf_evlist__mmap_read() Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
      Re: [PATCH 01/17] perf tools: Extract __perf_evlist__mmap_read() Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-13 15:10 +0200
    [PATCH 09/17] perf tools: Detect avalibility of write_backward Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
      Re: [PATCH 09/17] perf tools: Detect avalibility of write_backward Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-13 15:10 +0200
        Re: [PATCH 09/17] perf tools: Detect avalibility of write_backward "Wangnan (F)" <wangnan0@huawei.com> - 2016-05-20 17:40 +0200
          Re: [PATCH 09/17] perf tools: Detect avalibility of write_backward Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-20 17:40 +0200
    [PATCH 05/17] perf record: Prevent reading invalid data in record__mmap_read Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 17/17] perf tools: Don't warn about out of order event if write_backward is used Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 11/17] perf tools: Set write_backward attribut bit for overwrite events Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 04/17] perf tools: Operate multiple channels Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 08/17] perf record: Don't poll on overwrite channel Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
      Re: [PATCH 08/17] perf record: Don't poll on overwrite channel Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-13 15:20 +0200
        Re: [PATCH 08/17] perf record: Don't poll on overwrite channel "Wangnan (F)" <wangnan0@huawei.com> - 2016-05-16 05:20 +0200
    [PATCH 16/17] perf record: Toggle overwrite ring buffer for reading Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 10/17] perf tools: Enable overwrite settings Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
      Re: [PATCH 10/17] perf tools: Enable overwrite settings Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-16 15:40 +0200
    [PATCH 07/17] perf record: Don't read from and poll overwrite channel Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 12/17] perf tools: Record fd into perf_mmap Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 13/17] perf tools: Add API to pause a channel Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:00 +0200
    [PATCH 14/17] perf record: Rename variable to make code clear Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:10 +0200
    [PATCH 02/17] perf tools: Add evlist channel helpers Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:10 +0200
      Re: [PATCH 02/17] perf tools: Add evlist channel helpers Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-05-13 15:10 +0200
        Re: [PATCH 02/17] perf tools: Add evlist channel helpers "Wangnan (F)" <wangnan0@huawei.com> - 2016-05-18 05:40 +0200
          Re: [PATCH 02/17] perf tools: Add evlist channel helpers Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> - 2016-05-18 15:30 +0200
    [PATCH 03/17] perf tools: Automatically add new channel according to evlist Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:20 +0200
    [PATCH 06/17] perf tools: Squash overwrite setting into channel Wang Nan <wangnan0@huawei.com> - 2016-05-13 10:20 +0200

Page 2 of 2 — ← Prev page 1 [2]

#1400577 — [PATCH 13/17] perf tools: Add API to pause a channel

perf_evlist__channel_toggle_paused() is introduced to pause/resume a
channel in an evlist. Utilize PERF_EVENT_IOC_PAUSE_OUTPUT ioctl.
Following commits use perf_evlist__channel_toggle_paused() to ensure
overwrite ring buffer is turned off before reading.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/util/evlist.c | 28 ++++++++++++++++++++++++++++
 tools/perf/util/evlist.h |  2 ++
 2 files changed, 30 insertions(+)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 4295d7e..cfcd39a 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -706,6 +706,34 @@ int perf_evlist__channel_idx(struct perf_evlist *evlist,
 	return 0;
 }
 
+int perf_evlist__channel_toggle_paused(struct perf_evlist *evlist,
+				       int channel, bool pause)
+{
+	int i;
+
+	if (channel >= perf_evlist__channel_nr(evlist))
+		return -E2BIG;
+	if (!evlist->mmap)
+		return -EFAULT;
+	for (i = 0; i < evlist->nr_mmaps; i++) {
+		int n = channel * evlist->nr_mmaps + i;
+		int fd = evlist->mmap[n].fd;
+		int err;
+
+		if (fd < 0)
+			continue;
+		err = ioctl(fd, PERF_EVENT_IOC_PAUSE_OUTPUT,
+			    pause ? 1 : 0);
+		if (err) {
+			err = (errno == 0 ? -EINVAL : -errno);
+			pr_err("Unable to pause output on %d: %s\n",
+			       fd, strerror(-err));
+			return err;
+		}
+	}
+	return 0;
+}
+
 /* When check_messup is true, 'end' must points to a good entry */
 static union perf_event *
 perf_mmap__read(struct perf_mmap *md, bool check_messup, u64 start,
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index ee17449..2bb42fd 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -195,6 +195,8 @@ perf_evlist__get_mmap(struct perf_evlist *evlist,
 	return &evlist->mmap[idx];
 }
 
+int perf_evlist__channel_toggle_paused(struct perf_evlist *evlist,
+				       int channel, bool pause);
 int perf_evlist__open(struct perf_evlist *evlist);
 void perf_evlist__close(struct perf_evlist *evlist);
 
-- 
1.8.3.4

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#1400583 — [PATCH 14/17] perf record: Rename variable to make code clear

record__mmap_read() write data from ring buffer into perf.data.
'head' is maintained by kernel, points to the last writtend record.
'old' is maintained by perf, points to the record read in previous
round. record__mmap_read() saves data from 'old' to 'head' to
perf.data.

The names of these variables are not easy to read. In addition,
when dealing with backward writing ring buffer, the md->prev pointer
should point to 'head' instead of the last byte it got.

Add start and end pointer to make code clear and set md->prev to 'head'
instead of the moved 'old' pointer. This patch doesn't change
behavior since:

    buf = &data[old & md->mask];
    size = head - old;
    old += size;     <--- Here, old == head

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/builtin-record.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 49c41c3..9f4d3ad 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -88,17 +88,18 @@ static int record__mmap_read(struct record *rec, int idx)
 	struct perf_mmap *md = &rec->evlist->mmap[idx];
 	u64 head = perf_mmap__read_head(md);
 	u64 old = md->prev;
+	u64 end = head, start = old;
 	unsigned char *data = md->base + page_size;
 	unsigned long size;
 	void *buf;
 	int rc = 0;
 
-	if (old == head)
+	if (start == end)
 		return 0;
 
 	rec->samples++;
 
-	size = head - old;
+	size = end - start;
 	if (size > (unsigned long)(md->mask) + 1) {
 		WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");
 
@@ -107,10 +108,10 @@ static int record__mmap_read(struct record *rec, int idx)
 		return 0;
 	}
 
-	if ((old & md->mask) + size != (head & md->mask)) {
-		buf = &data[old & md->mask];
-		size = md->mask + 1 - (old & md->mask);
-		old += size;
+	if ((start & md->mask) + size != (end & md->mask)) {
+		buf = &data[start & md->mask];
+		size = md->mask + 1 - (start & md->mask);
+		start += size;
 
 		if (record__write(rec, buf, size) < 0) {
 			rc = -1;
@@ -118,16 +119,16 @@ static int record__mmap_read(struct record *rec, int idx)
 		}
 	}
 
-	buf = &data[old & md->mask];
-	size = head - old;
-	old += size;
+	buf = &data[start & md->mask];
+	size = end - start;
+	start += size;
 
 	if (record__write(rec, buf, size) < 0) {
 		rc = -1;
 		goto out;
 	}
 
-	md->prev = old;
+	md->prev = head;
 	perf_evlist__mmap_consume(rec->evlist, idx);
 out:
 	return rc;
-- 
1.8.3.4

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#1400587 — [PATCH 02/17] perf tools: Add evlist channel helpers

In this commit sereval helpers are introduced to support the principle
of channel. Channels hold different groups of evsels which configured
differently. It will be used for overwritable evsels, which allows perf
record some events continuously while capture snapshot for other events
when something happen. Tracking events (mmap, mmap2, fork, exit ...)
are another possible events worth to be put into a separated channel.

Channels are represented by an array with channel flags. Each channel
contains evlist->nr_mmaps mmaps. Channels are configured before
perf_evlist__mmap_ex(). During that function nr_mmaps mmaps for each
channel are allocated together as a big array.
perf_evlist__channel_idx() converts index in the big array and the
channel number. For API functions which accept idx, _ex() versions are
introduced to accept selecting an mmap from a channel.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/builtin-record.c |   6 ++
 tools/perf/util/evlist.c    | 130 ++++++++++++++++++++++++++++++++++++++++++--
 tools/perf/util/evlist.h    |  58 ++++++++++++++++++++
 3 files changed, 188 insertions(+), 6 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f3679c4..6e44834 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -316,6 +316,12 @@ try_again:
 		goto out;
 	}
 
+	perf_evlist__channel_reset(evlist);
+	rc = perf_evlist__channel_add(evlist, 0, true);
+	if (rc < 0)
+		goto out;
+	rc = 0;
+
 	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, false,
 				 opts->auxtrace_mmap_pages,
 				 opts->auxtrace_snapshot_mode) < 0) {
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 5e86972..6c11b9e 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -679,6 +679,33 @@ static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist,
 	return NULL;
 }
 
+int perf_evlist__channel_idx(struct perf_evlist *evlist,
+			     int *p_channel, int *p_idx)
+{
+	int channel = *p_channel;
+	int _idx = *p_idx;
+
+	if (_idx < 0)
+		return -EINVAL;
+	/*
+	 * Negative channel means caller explicitly use real index.
+	 */
+	if (channel < 0) {
+		channel = perf_evlist__idx_channel(evlist, _idx);
+		_idx = _idx % evlist->nr_mmaps;
+	}
+	if (channel < 0)
+		return channel;
+	if (channel >= PERF_EVLIST__NR_CHANNELS)
+		return -E2BIG;
+	if (_idx >= evlist->nr_mmaps)
+		return -E2BIG;
+
+	*p_channel = channel;
+	*p_idx = evlist->nr_mmaps * channel + _idx;
+	return 0;
+}
+
 /* When check_messup is true, 'end' must points to a good entry */
 static union perf_event *
 perf_mmap__read(struct perf_mmap *md, bool check_messup, u64 start,
@@ -756,11 +783,19 @@ __perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head,
 	return perf_mmap__read(md, overwrite, old, head, prev);
 }
 
-union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
+union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
+					    int channel, int idx)
 {
 	struct perf_mmap *md = &evlist->mmap[idx];
-	u64 head;
-	u64 old = md->prev;
+	u64 head, old;
+	int err = perf_evlist__channel_idx(evlist, &channel, &idx);
+
+	if (err || !perf_evlist__channel_is_enabled(evlist, channel)) {
+		pr_err("ERROR: invalid mmap index: channel %d, idx: %d\n",
+		       channel, idx);
+		return NULL;
+	}
+	old = md->prev;
 
 	/*
 	 * Check if event was unmapped due to a POLLHUP/POLLERR.
@@ -824,6 +859,11 @@ void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx)
 	md->prev = head;
 }
 
+union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
+{
+	return perf_evlist__mmap_read_ex(evlist, -1, idx);
+}
+
 static bool perf_mmap__empty(struct perf_mmap *md)
 {
 	return perf_mmap__read_head(md) == md->prev && !md->auxtrace_mmap.base;
@@ -842,10 +882,18 @@ static void perf_evlist__mmap_put(struct perf_evlist *evlist, int idx)
 		__perf_evlist__munmap(evlist, idx);
 }
 
-void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
+void perf_evlist__mmap_consume_ex(struct perf_evlist *evlist,
+				  int channel, int idx)
 {
+	int err = perf_evlist__channel_idx(evlist, &channel, &idx);
 	struct perf_mmap *md = &evlist->mmap[idx];
 
+	if (err || !perf_evlist__channel_is_enabled(evlist, channel)) {
+		pr_err("ERROR: invalid mmap index: channel %d, idx: %d\n",
+		       channel, idx);
+		return;
+	}
+
 	if (!evlist->overwrite) {
 		u64 old = md->prev;
 
@@ -856,6 +904,11 @@ void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
 		perf_evlist__mmap_put(evlist, idx);
 }
 
+void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
+{
+	perf_evlist__mmap_consume_ex(evlist, -1, idx);
+}
+
 int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
 			       struct auxtrace_mmap_params *mp __maybe_unused,
 			       void *userpg __maybe_unused,
@@ -901,7 +954,7 @@ void perf_evlist__munmap(struct perf_evlist *evlist)
 	if (evlist->mmap == NULL)
 		return;
 
-	for (i = 0; i < evlist->nr_mmaps; i++)
+	for (i = 0; i < perf_evlist__mmap_nr(evlist); i++)
 		__perf_evlist__munmap(evlist, i);
 
 	zfree(&evlist->mmap);
@@ -909,10 +962,17 @@ void perf_evlist__munmap(struct perf_evlist *evlist)
 
 static int perf_evlist__alloc_mmap(struct perf_evlist *evlist)
 {
+	int total_mmaps;
+
 	evlist->nr_mmaps = cpu_map__nr(evlist->cpus);
 	if (cpu_map__empty(evlist->cpus))
 		evlist->nr_mmaps = thread_map__nr(evlist->threads);
-	evlist->mmap = zalloc(evlist->nr_mmaps * sizeof(struct perf_mmap));
+
+	total_mmaps = perf_evlist__mmap_nr(evlist);
+	if (!total_mmaps)
+		return -EINVAL;
+
+	evlist->mmap = zalloc(total_mmaps * sizeof(struct perf_mmap));
 	return evlist->mmap != NULL ? 0 : -ENOMEM;
 }
 
@@ -1221,6 +1281,12 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
 		      bool overwrite)
 {
+	int err;
+
+	perf_evlist__channel_reset(evlist);
+	err = perf_evlist__channel_add(evlist, 0, true);
+	if (err < 0)
+		return err;
 	return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
 }
 
@@ -1862,3 +1928,55 @@ perf_evlist__find_evsel_by_str(struct perf_evlist *evlist,
 
 	return NULL;
 }
+
+int perf_evlist__channel_nr(struct perf_evlist *evlist)
+{
+	int i;
+
+	for (i = PERF_EVLIST__NR_CHANNELS - 1; i >= 0; i--) {
+		unsigned long flags = evlist->channel_flags[i];
+
+		if (flags & PERF_EVLIST__CHANNEL_ENABLED)
+			return i + 1;
+	}
+	return 0;
+}
+
+int perf_evlist__mmap_nr(struct perf_evlist *evlist)
+{
+	return evlist->nr_mmaps * perf_evlist__channel_nr(evlist);
+}
+
+void perf_evlist__channel_reset(struct perf_evlist *evlist)
+{
+	int i;
+
+	BUG_ON(evlist->mmap);
+
+	for (i = 0; i < PERF_EVLIST__NR_CHANNELS; i++)
+		evlist->channel_flags[i] = 0;
+}
+
+int perf_evlist__channel_add(struct perf_evlist *evlist,
+			     unsigned long flag,
+			     bool is_default)
+{
+	int n = perf_evlist__channel_nr(evlist);
+	unsigned long *flags = evlist->channel_flags;
+
+	BUG_ON(evlist->mmap);
+
+	if (n >= PERF_EVLIST__NR_CHANNELS) {
+		pr_debug("ERROR: too many channels. Increase PERF_EVLIST__NR_CHANNELS\n");
+		return -ENOSPC;
+	}
+
+	if (is_default) {
+		memmove(&flags[1], &flags[0],
+			sizeof(evlist->channel_flags) -
+			sizeof(evlist->channel_flags[0]));
+		n = 0;
+	}
+	flags[n] = flag | PERF_EVLIST__CHANNEL_ENABLED;
+	return n;
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 85d1b59..4cb5d3a 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -20,6 +20,11 @@ struct record_opts;
 #define PERF_EVLIST__HLIST_BITS 8
 #define PERF_EVLIST__HLIST_SIZE (1 << PERF_EVLIST__HLIST_BITS)
 
+#define PERF_EVLIST__NR_CHANNELS	1
+enum perf_evlist_mmap_flag {
+	PERF_EVLIST__CHANNEL_ENABLED	= 1,
+};
+
 /**
  * struct perf_mmap - perf's ring buffer mmap details
  *
@@ -52,6 +57,7 @@ struct perf_evlist {
 		pid_t	pid;
 	} workload;
 	struct fdarray	 pollfd;
+	unsigned long channel_flags[PERF_EVLIST__NR_CHANNELS];
 	struct perf_mmap *mmap;
 	struct thread_map *threads;
 	struct cpu_map	  *cpus;
@@ -127,13 +133,65 @@ struct perf_evsel *perf_evlist__id2evsel_strict(struct perf_evlist *evlist,
 
 struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id);
 
+union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
+					    int channel, int idx);
 union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx);
 
 union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist,
 						  int idx);
 void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx);
 
+void perf_evlist__mmap_consume_ex(struct perf_evlist *evlist,
+				  int channel, int idx);
 void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx);
+int perf_evlist__mmap_nr(struct perf_evlist *evlist);
+
+int perf_evlist__channel_nr(struct perf_evlist *evlist);
+void perf_evlist__channel_reset(struct perf_evlist *evlist);
+int perf_evlist__channel_add(struct perf_evlist *evlist,
+			     unsigned long flag,
+			     bool is_default);
+
+static inline bool
+__perf_evlist__channel_check(struct perf_evlist *evlist, int channel,
+			     enum perf_evlist_mmap_flag bits)
+{
+	if (channel >= PERF_EVLIST__NR_CHANNELS)
+		return false;
+
+	return (evlist->channel_flags[channel] & bits) ? true : false;
+}
+#define perf_evlist__channel_check(e, c, b) \
+		__perf_evlist__channel_check(e, c, PERF_EVLIST__CHANNEL_##b)
+
+static inline bool
+perf_evlist__channel_is_enabled(struct perf_evlist *evlist, int channel)
+{
+	return perf_evlist__channel_check(evlist, channel, ENABLED);
+}
+
+static inline int
+perf_evlist__idx_channel(struct perf_evlist *evlist, int idx)
+{
+	int channel = idx / evlist->nr_mmaps;
+
+	if (channel >= PERF_EVLIST__NR_CHANNELS)
+		return -E2BIG;
+	return channel;
+}
+
+int perf_evlist__channel_idx(struct perf_evlist *evlist,
+			     int *p_channel, int *p_idx);
+
+static inline struct perf_mmap *
+perf_evlist__get_mmap(struct perf_evlist *evlist,
+		      int channel, int idx)
+{
+	if (perf_evlist__channel_idx(evlist, &channel, &idx))
+		return NULL;
+
+	return &evlist->mmap[idx];
+}
 
 int perf_evlist__open(struct perf_evlist *evlist);
 void perf_evlist__close(struct perf_evlist *evlist);
-- 
1.8.3.4

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#1400780 — Re: [PATCH 02/17] perf tools: Add evlist channel helpers

Em Fri, May 13, 2016 at 07:55:59AM +0000, Wang Nan escreveu:
> In this commit sereval helpers are introduced to support the principle

                 several

> of channel. Channels hold different groups of evsels which configured
> differently. It will be used for overwritable evsels, which allows perf

why not use multiple evlists? An "evlist" is a "list of evsels", why do
we need yet another way of grouping evlists?

- Arnaldo

> record some events continuously while capture snapshot for other events
> when something happen. Tracking events (mmap, mmap2, fork, exit ...)
> are another possible events worth to be put into a separated channel.
> 
> Channels are represented by an array with channel flags. Each channel
> contains evlist->nr_mmaps mmaps. Channels are configured before
> perf_evlist__mmap_ex(). During that function nr_mmaps mmaps for each
> channel are allocated together as a big array.
> perf_evlist__channel_idx() converts index in the big array and the
> channel number. For API functions which accept idx, _ex() versions are
> introduced to accept selecting an mmap from a channel.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Signed-off-by: He Kuang <hekuang@huawei.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> ---
>  tools/perf/builtin-record.c |   6 ++
>  tools/perf/util/evlist.c    | 130 ++++++++++++++++++++++++++++++++++++++++++--
>  tools/perf/util/evlist.h    |  58 ++++++++++++++++++++
>  3 files changed, 188 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index f3679c4..6e44834 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -316,6 +316,12 @@ try_again:
>  		goto out;
>  	}
>  
> +	perf_evlist__channel_reset(evlist);
> +	rc = perf_evlist__channel_add(evlist, 0, true);
> +	if (rc < 0)
> +		goto out;
> +	rc = 0;
> +
>  	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, false,
>  				 opts->auxtrace_mmap_pages,
>  				 opts->auxtrace_snapshot_mode) < 0) {
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 5e86972..6c11b9e 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -679,6 +679,33 @@ static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist,
>  	return NULL;
>  }
>  
> +int perf_evlist__channel_idx(struct perf_evlist *evlist,
> +			     int *p_channel, int *p_idx)
> +{
> +	int channel = *p_channel;
> +	int _idx = *p_idx;
> +
> +	if (_idx < 0)
> +		return -EINVAL;
> +	/*
> +	 * Negative channel means caller explicitly use real index.
> +	 */
> +	if (channel < 0) {
> +		channel = perf_evlist__idx_channel(evlist, _idx);
> +		_idx = _idx % evlist->nr_mmaps;
> +	}
> +	if (channel < 0)
> +		return channel;
> +	if (channel >= PERF_EVLIST__NR_CHANNELS)
> +		return -E2BIG;
> +	if (_idx >= evlist->nr_mmaps)
> +		return -E2BIG;
> +
> +	*p_channel = channel;
> +	*p_idx = evlist->nr_mmaps * channel + _idx;
> +	return 0;
> +}
> +
>  /* When check_messup is true, 'end' must points to a good entry */
>  static union perf_event *
>  perf_mmap__read(struct perf_mmap *md, bool check_messup, u64 start,
> @@ -756,11 +783,19 @@ __perf_evlist__mmap_read(struct perf_mmap *md, bool overwrite, u64 head,
>  	return perf_mmap__read(md, overwrite, old, head, prev);
>  }
>  
> -union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
> +union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
> +					    int channel, int idx)
>  {
>  	struct perf_mmap *md = &evlist->mmap[idx];
> -	u64 head;
> -	u64 old = md->prev;
> +	u64 head, old;
> +	int err = perf_evlist__channel_idx(evlist, &channel, &idx);
> +
> +	if (err || !perf_evlist__channel_is_enabled(evlist, channel)) {
> +		pr_err("ERROR: invalid mmap index: channel %d, idx: %d\n",
> +		       channel, idx);
> +		return NULL;
> +	}
> +	old = md->prev;
>  
>  	/*
>  	 * Check if event was unmapped due to a POLLHUP/POLLERR.
> @@ -824,6 +859,11 @@ void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx)
>  	md->prev = head;
>  }
>  
> +union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
> +{
> +	return perf_evlist__mmap_read_ex(evlist, -1, idx);
> +}
> +
>  static bool perf_mmap__empty(struct perf_mmap *md)
>  {
>  	return perf_mmap__read_head(md) == md->prev && !md->auxtrace_mmap.base;
> @@ -842,10 +882,18 @@ static void perf_evlist__mmap_put(struct perf_evlist *evlist, int idx)
>  		__perf_evlist__munmap(evlist, idx);
>  }
>  
> -void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
> +void perf_evlist__mmap_consume_ex(struct perf_evlist *evlist,
> +				  int channel, int idx)
>  {
> +	int err = perf_evlist__channel_idx(evlist, &channel, &idx);
>  	struct perf_mmap *md = &evlist->mmap[idx];
>  
> +	if (err || !perf_evlist__channel_is_enabled(evlist, channel)) {
> +		pr_err("ERROR: invalid mmap index: channel %d, idx: %d\n",
> +		       channel, idx);
> +		return;
> +	}
> +
>  	if (!evlist->overwrite) {
>  		u64 old = md->prev;
>  
> @@ -856,6 +904,11 @@ void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
>  		perf_evlist__mmap_put(evlist, idx);
>  }
>  
> +void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx)
> +{
> +	perf_evlist__mmap_consume_ex(evlist, -1, idx);
> +}
> +
>  int __weak auxtrace_mmap__mmap(struct auxtrace_mmap *mm __maybe_unused,
>  			       struct auxtrace_mmap_params *mp __maybe_unused,
>  			       void *userpg __maybe_unused,
> @@ -901,7 +954,7 @@ void perf_evlist__munmap(struct perf_evlist *evlist)
>  	if (evlist->mmap == NULL)
>  		return;
>  
> -	for (i = 0; i < evlist->nr_mmaps; i++)
> +	for (i = 0; i < perf_evlist__mmap_nr(evlist); i++)
>  		__perf_evlist__munmap(evlist, i);
>  
>  	zfree(&evlist->mmap);
> @@ -909,10 +962,17 @@ void perf_evlist__munmap(struct perf_evlist *evlist)
>  
>  static int perf_evlist__alloc_mmap(struct perf_evlist *evlist)
>  {
> +	int total_mmaps;
> +
>  	evlist->nr_mmaps = cpu_map__nr(evlist->cpus);
>  	if (cpu_map__empty(evlist->cpus))
>  		evlist->nr_mmaps = thread_map__nr(evlist->threads);
> -	evlist->mmap = zalloc(evlist->nr_mmaps * sizeof(struct perf_mmap));
> +
> +	total_mmaps = perf_evlist__mmap_nr(evlist);
> +	if (!total_mmaps)
> +		return -EINVAL;
> +
> +	evlist->mmap = zalloc(total_mmaps * sizeof(struct perf_mmap));
>  	return evlist->mmap != NULL ? 0 : -ENOMEM;
>  }
>  
> @@ -1221,6 +1281,12 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
>  int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
>  		      bool overwrite)
>  {
> +	int err;
> +
> +	perf_evlist__channel_reset(evlist);
> +	err = perf_evlist__channel_add(evlist, 0, true);
> +	if (err < 0)
> +		return err;
>  	return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
>  }
>  
> @@ -1862,3 +1928,55 @@ perf_evlist__find_evsel_by_str(struct perf_evlist *evlist,
>  
>  	return NULL;
>  }
> +
> +int perf_evlist__channel_nr(struct perf_evlist *evlist)
> +{
> +	int i;
> +
> +	for (i = PERF_EVLIST__NR_CHANNELS - 1; i >= 0; i--) {
> +		unsigned long flags = evlist->channel_flags[i];
> +
> +		if (flags & PERF_EVLIST__CHANNEL_ENABLED)
> +			return i + 1;
> +	}
> +	return 0;
> +}
> +
> +int perf_evlist__mmap_nr(struct perf_evlist *evlist)
> +{
> +	return evlist->nr_mmaps * perf_evlist__channel_nr(evlist);
> +}
> +
> +void perf_evlist__channel_reset(struct perf_evlist *evlist)
> +{
> +	int i;
> +
> +	BUG_ON(evlist->mmap);
> +
> +	for (i = 0; i < PERF_EVLIST__NR_CHANNELS; i++)
> +		evlist->channel_flags[i] = 0;
> +}
> +
> +int perf_evlist__channel_add(struct perf_evlist *evlist,
> +			     unsigned long flag,
> +			     bool is_default)
> +{
> +	int n = perf_evlist__channel_nr(evlist);
> +	unsigned long *flags = evlist->channel_flags;
> +
> +	BUG_ON(evlist->mmap);
> +
> +	if (n >= PERF_EVLIST__NR_CHANNELS) {
> +		pr_debug("ERROR: too many channels. Increase PERF_EVLIST__NR_CHANNELS\n");
> +		return -ENOSPC;
> +	}
> +
> +	if (is_default) {
> +		memmove(&flags[1], &flags[0],
> +			sizeof(evlist->channel_flags) -
> +			sizeof(evlist->channel_flags[0]));
> +		n = 0;
> +	}
> +	flags[n] = flag | PERF_EVLIST__CHANNEL_ENABLED;
> +	return n;
> +}
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 85d1b59..4cb5d3a 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -20,6 +20,11 @@ struct record_opts;
>  #define PERF_EVLIST__HLIST_BITS 8
>  #define PERF_EVLIST__HLIST_SIZE (1 << PERF_EVLIST__HLIST_BITS)
>  
> +#define PERF_EVLIST__NR_CHANNELS	1
> +enum perf_evlist_mmap_flag {
> +	PERF_EVLIST__CHANNEL_ENABLED	= 1,
> +};
> +
>  /**
>   * struct perf_mmap - perf's ring buffer mmap details
>   *
> @@ -52,6 +57,7 @@ struct perf_evlist {
>  		pid_t	pid;
>  	} workload;
>  	struct fdarray	 pollfd;
> +	unsigned long channel_flags[PERF_EVLIST__NR_CHANNELS];
>  	struct perf_mmap *mmap;
>  	struct thread_map *threads;
>  	struct cpu_map	  *cpus;
> @@ -127,13 +133,65 @@ struct perf_evsel *perf_evlist__id2evsel_strict(struct perf_evlist *evlist,
>  
>  struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id);
>  
> +union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
> +					    int channel, int idx);
>  union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx);
>  
>  union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist,
>  						  int idx);
>  void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx);
>  
> +void perf_evlist__mmap_consume_ex(struct perf_evlist *evlist,
> +				  int channel, int idx);
>  void perf_evlist__mmap_consume(struct perf_evlist *evlist, int idx);
> +int perf_evlist__mmap_nr(struct perf_evlist *evlist);
> +
> +int perf_evlist__channel_nr(struct perf_evlist *evlist);
> +void perf_evlist__channel_reset(struct perf_evlist *evlist);
> +int perf_evlist__channel_add(struct perf_evlist *evlist,
> +			     unsigned long flag,
> +			     bool is_default);
> +
> +static inline bool
> +__perf_evlist__channel_check(struct perf_evlist *evlist, int channel,
> +			     enum perf_evlist_mmap_flag bits)
> +{
> +	if (channel >= PERF_EVLIST__NR_CHANNELS)
> +		return false;
> +
> +	return (evlist->channel_flags[channel] & bits) ? true : false;
> +}
> +#define perf_evlist__channel_check(e, c, b) \
> +		__perf_evlist__channel_check(e, c, PERF_EVLIST__CHANNEL_##b)
> +
> +static inline bool
> +perf_evlist__channel_is_enabled(struct perf_evlist *evlist, int channel)
> +{
> +	return perf_evlist__channel_check(evlist, channel, ENABLED);
> +}
> +
> +static inline int
> +perf_evlist__idx_channel(struct perf_evlist *evlist, int idx)
> +{
> +	int channel = idx / evlist->nr_mmaps;
> +
> +	if (channel >= PERF_EVLIST__NR_CHANNELS)
> +		return -E2BIG;
> +	return channel;
> +}
> +
> +int perf_evlist__channel_idx(struct perf_evlist *evlist,
> +			     int *p_channel, int *p_idx);
> +
> +static inline struct perf_mmap *
> +perf_evlist__get_mmap(struct perf_evlist *evlist,
> +		      int channel, int idx)
> +{
> +	if (perf_evlist__channel_idx(evlist, &channel, &idx))
> +		return NULL;
> +
> +	return &evlist->mmap[idx];
> +}
>  
>  int perf_evlist__open(struct perf_evlist *evlist);
>  void perf_evlist__close(struct perf_evlist *evlist);
> -- 
> 1.8.3.4

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#1402709 — Re: [PATCH 02/17] perf tools: Add evlist channel helpers

On 2016/5/13 21:05, Arnaldo Carvalho de Melo wrote:
> Em Fri, May 13, 2016 at 07:55:59AM +0000, Wang Nan escreveu:
>> In this commit sereval helpers are introduced to support the principle
>                   several
>
>> of channel. Channels hold different groups of evsels which configured
>> differently. It will be used for overwritable evsels, which allows perf
> why not use multiple evlists? An "evlist" is a "list of evsels", why do
> we need yet another way of grouping evlists?
>
> - Arnaldo
>

There's an assumption all over perf that there's only one evlist: in 
'struct record'
there's an 'evlist' pointer, in 'struct session' there's also an 
'evlist' pointer.
Trying to change them to an array results in 181 errors, so I think 
fundamentally
moving to multiple evlists is nearly impossible.

Now I'm thinking introducing auxiliary evlists to perf record. We still 
obey one
evlist assumption, only creates separated evlists for mmap.

Thank you.

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#1402976 — Re: [PATCH 02/17] perf tools: Add evlist channel helpers

Em Wed, May 18, 2016 at 11:27:43AM +0800, Wangnan (F) escreveu:
> On 2016/5/13 21:05, Arnaldo Carvalho de Melo wrote:
> >Em Fri, May 13, 2016 at 07:55:59AM +0000, Wang Nan escreveu:
> >> Channels hold different groups of evsels which configured
> >> differently. It will be used for overwritable evsels, which allows
> >> perf

> >why not use multiple evlists? An "evlist" is a "list of evsels", why do
> >we need yet another way of grouping evlists?
 
> There's an assumption all over perf that there's only one evlist: in
> 'struct record' there's an 'evlist' pointer, in 'struct session'
> there's also an 'evlist' pointer.

Well, at some point there were none, and multiple tools used multiple
ways to deal with lists of events :-)

> Trying to change them to an array results in 181 errors, so I think
> fundamentally moving to multiple evlists is nearly impossible.

Well, in the next paragraph you give it some hope :-)
 
> Now I'm thinking introducing auxiliary evlists to perf record. We
> still obey one evlist assumption, only creates separated evlists for
> mmap.

Ok, that may be the way to go, i.e. linking evlists somehow for some
specific use cases, i.e. consuming events from multiple evlists,
probably sorting them via the ordered_events class, etc.

I have to review this more deeply to try and come with suggestions :-\

- Arnaldo

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#1400603 — [PATCH 03/17] perf tools: Automatically add new channel according to evlist

perf_evlist__channel_find() can be used to find a proper channel based
on propreties of a evsel. If the channel doesn't exist, it can create
new one for it. After this patch there's no need to create default
channel explicitly.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/builtin-record.c |  5 -----
 tools/perf/util/evlist.c    | 47 ++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 6e44834..3140378 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -317,11 +317,6 @@ try_again:
 	}
 
 	perf_evlist__channel_reset(evlist);
-	rc = perf_evlist__channel_add(evlist, 0, true);
-	if (rc < 0)
-		goto out;
-	rc = 0;
-
 	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, false,
 				 opts->auxtrace_mmap_pages,
 				 opts->auxtrace_snapshot_mode) < 0) {
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 6c11b9e..47a8f1f 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1017,6 +1017,43 @@ static int __perf_evlist__mmap(struct perf_evlist *evlist, int idx,
 	return 0;
 }
 
+static unsigned long
+perf_evlist__channel_for_evsel(struct perf_evsel *evsel __maybe_unused)
+{
+	return 0;
+}
+
+static int
+perf_evlist__channel_find(struct perf_evlist *evlist,
+			  struct perf_evsel *evsel,
+			  bool add_new)
+{
+	unsigned long flag = perf_evlist__channel_for_evsel(evsel);
+	int i;
+
+	flag |= PERF_EVLIST__CHANNEL_ENABLED;
+	for (i = 0; i < perf_evlist__channel_nr(evlist); i++)
+		if (evlist->channel_flags[i] == flag)
+			return i;
+	if (add_new)
+		return perf_evlist__channel_add(evlist, flag, false);
+	return -ENOENT;
+}
+
+static int
+perf_evlist__channel_complete(struct perf_evlist *evlist)
+{
+	struct perf_evsel *evsel;
+	int err;
+
+	evlist__for_each(evlist, evsel) {
+		err = perf_evlist__channel_find(evlist, evsel, true);
+		if (err < 0)
+			return err;
+	}
+	return 0;
+}
+
 static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
 				       struct mmap_params *mp, int cpu,
 				       int thread, int *output)
@@ -1244,6 +1281,7 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 			 bool overwrite, unsigned int auxtrace_pages,
 			 bool auxtrace_overwrite)
 {
+	int err;
 	struct perf_evsel *evsel;
 	const struct cpu_map *cpus = evlist->cpus;
 	const struct thread_map *threads = evlist->threads;
@@ -1251,6 +1289,10 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 		.prot = PROT_READ | (overwrite ? 0 : PROT_WRITE),
 	};
 
+	err = perf_evlist__channel_complete(evlist);
+	if (err)
+		return err;
+
 	if (evlist->mmap == NULL && perf_evlist__alloc_mmap(evlist) < 0)
 		return -ENOMEM;
 
@@ -1281,12 +1323,7 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
 		      bool overwrite)
 {
-	int err;
-
 	perf_evlist__channel_reset(evlist);
-	err = perf_evlist__channel_add(evlist, 0, true);
-	if (err < 0)
-		return err;
 	return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
 }
 
-- 
1.8.3.4

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#1400604 — [PATCH 06/17] perf tools: Squash overwrite setting into channel

Make 'overwrite' a channel configuration other than a evlist global
option. With this setting an evlist can have two channels, one is
normal channel, another is overwritable channel.
perf_evlist__channel_for_evsel() ensures events with 'overwrite'
configuration inserted to overwritable channel.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/builtin-record.c |  2 +-
 tools/perf/util/evlist.c    | 43 ++++++++++++++++++++++++++++---------------
 tools/perf/util/evlist.h    |  7 +++----
 tools/perf/util/evsel.h     |  1 +
 4 files changed, 33 insertions(+), 20 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 81c700d..5e87602 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -325,7 +325,7 @@ try_again:
 	}
 
 	perf_evlist__channel_reset(evlist);
-	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages, false,
+	if (perf_evlist__mmap_ex(evlist, opts->mmap_pages,
 				 opts->auxtrace_mmap_pages,
 				 opts->auxtrace_snapshot_mode) < 0) {
 		if (errno == EPERM) {
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index eefa33b..abce588 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -789,6 +789,7 @@ union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
 	struct perf_mmap *md = &evlist->mmap[idx];
 	u64 head, old;
 	int err = perf_evlist__channel_idx(evlist, &channel, &idx);
+	bool rdonly;
 
 	if (err || !perf_evlist__channel_is_enabled(evlist, channel)) {
 		pr_err("ERROR: invalid mmap index: channel %d, idx: %d\n",
@@ -805,8 +806,8 @@ union perf_event *perf_evlist__mmap_read_ex(struct perf_evlist *evlist,
 
 	head = perf_mmap__read_head(md);
 
-	return __perf_evlist__mmap_read(md, evlist->overwrite, head,
-					old, &md->prev);
+	rdonly = perf_evlist__channel_check(evlist, channel, RDONLY);
+	return __perf_evlist__mmap_read(md, rdonly, old, head, &md->prev);
 }
 
 union perf_event *
@@ -894,7 +895,7 @@ void perf_evlist__mmap_consume_ex(struct perf_evlist *evlist,
 		return;
 	}
 
-	if (!evlist->overwrite) {
+	if (!perf_evlist__channel_check(evlist, channel, RDONLY)) {
 		u64 old = md->prev;
 
 		perf_mmap__write_tail(md, old);
@@ -987,7 +988,6 @@ static int perf_evlist__alloc_mmap(struct perf_evlist *evlist)
 }
 
 struct mmap_params {
-	int prot;
 	int mask;
 	struct auxtrace_mmap_params auxtrace_mp;
 };
@@ -995,6 +995,15 @@ struct mmap_params {
 static int __perf_evlist__mmap(struct perf_evlist *evlist, int idx,
 			       struct mmap_params *mp, int fd)
 {
+	int channel = perf_evlist__idx_channel(evlist, idx);
+	int prot = PROT_READ;
+
+	if (channel < 0)
+		return -1;
+
+	if (!perf_evlist__channel_check(evlist, channel, RDONLY))
+		prot |= PROT_WRITE;
+
 	/*
 	 * The last one will be done at perf_evlist__mmap_consume(), so that we
 	 * make sure we don't prevent tools from consuming every last event in
@@ -1011,7 +1020,7 @@ static int __perf_evlist__mmap(struct perf_evlist *evlist, int idx,
 	atomic_set(&evlist->mmap[idx].refcnt, 2);
 	evlist->mmap[idx].prev = 0;
 	evlist->mmap[idx].mask = mp->mask;
-	evlist->mmap[idx].base = mmap(NULL, evlist->mmap_len, mp->prot,
+	evlist->mmap[idx].base = mmap(NULL, evlist->mmap_len, prot,
 				      MAP_SHARED, fd, 0);
 	if (evlist->mmap[idx].base == MAP_FAILED) {
 		pr_debug2("failed to mmap perf event ring buffer, error %d\n",
@@ -1030,7 +1039,11 @@ static int __perf_evlist__mmap(struct perf_evlist *evlist, int idx,
 static unsigned long
 perf_evlist__channel_for_evsel(struct perf_evsel *evsel __maybe_unused)
 {
-	return 0;
+	unsigned long flag = 0;
+
+	if (evsel->overwrite)
+		flag |= PERF_EVLIST__CHANNEL_RDONLY;
+	return flag;
 }
 
 static int
@@ -1286,11 +1299,10 @@ int perf_evlist__parse_mmap_pages(const struct option *opt, const char *str,
  * perf_evlist__mmap_ex - Create mmaps to receive events.
  * @evlist: list of events
  * @pages: map length in pages
- * @overwrite: overwrite older events?
  * @auxtrace_pages - auxtrace map length in pages
  * @auxtrace_overwrite - overwrite older auxtrace data?
  *
- * If @overwrite is %false the user needs to signal event consumption using
+ * For writable channel, the user needs to signal event consumption using
  * perf_mmap__write_tail().  Using perf_evlist__mmap_read() does this
  * automatically.
  *
@@ -1300,16 +1312,13 @@ int perf_evlist__parse_mmap_pages(const struct option *opt, const char *str,
  * Return: %0 on success, negative error code otherwise.
  */
 int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
-			 bool overwrite, unsigned int auxtrace_pages,
-			 bool auxtrace_overwrite)
+			 unsigned int auxtrace_pages, bool auxtrace_overwrite)
 {
 	int err;
 	struct perf_evsel *evsel;
 	const struct cpu_map *cpus = evlist->cpus;
 	const struct thread_map *threads = evlist->threads;
-	struct mmap_params mp = {
-		.prot = PROT_READ | (overwrite ? 0 : PROT_WRITE),
-	};
+	struct mmap_params mp;
 
 	err = perf_evlist__channel_complete(evlist);
 	if (err)
@@ -1321,7 +1330,6 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 	if (evlist->pollfd.entries == NULL && perf_evlist__alloc_pollfd(evlist) < 0)
 		return -ENOMEM;
 
-	evlist->overwrite = overwrite;
 	evlist->mmap_len = perf_evlist__mmap_size(pages);
 	pr_debug("mmap size %zuB\n", evlist->mmap_len);
 	mp.mask = evlist->mmap_len - page_size - 1;
@@ -1345,8 +1353,13 @@ int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
 int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
 		      bool overwrite)
 {
+	struct perf_evsel *evsel;
+
 	perf_evlist__channel_reset(evlist);
-	return perf_evlist__mmap_ex(evlist, pages, overwrite, 0, false);
+	evlist__for_each(evlist, evsel)
+		evsel->overwrite = overwrite;
+
+	return perf_evlist__mmap_ex(evlist, pages, 0, false);
 }
 
 int perf_evlist__create_maps(struct perf_evlist *evlist, struct target *target)
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 188f0c7..c53bdbd 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -20,9 +20,10 @@ struct record_opts;
 #define PERF_EVLIST__HLIST_BITS 8
 #define PERF_EVLIST__HLIST_SIZE (1 << PERF_EVLIST__HLIST_BITS)
 
-#define PERF_EVLIST__NR_CHANNELS	2
+#define PERF_EVLIST__NR_CHANNELS	3
 enum perf_evlist_mmap_flag {
 	PERF_EVLIST__CHANNEL_ENABLED	= 1,
+	PERF_EVLIST__CHANNEL_RDONLY	= 2,
 };
 
 /**
@@ -45,7 +46,6 @@ struct perf_evlist {
 	int		 nr_entries;
 	int		 nr_groups;
 	int		 nr_mmaps;
-	bool		 overwrite;
 	bool		 enabled;
 	bool		 has_user_cpus;
 	size_t		 mmap_len;
@@ -223,8 +223,7 @@ int perf_evlist__parse_mmap_pages(const struct option *opt,
 unsigned long perf_event_mlock_kb_in_pages(void);
 
 int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
-			 bool overwrite, unsigned int auxtrace_pages,
-			 bool auxtrace_overwrite);
+			 unsigned int auxtrace_pages, bool auxtrace_overwrite);
 int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
 		      bool overwrite);
 void perf_evlist__munmap(struct perf_evlist *evlist);
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 8a644fe..c1f1015 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -112,6 +112,7 @@ struct perf_evsel {
 	bool			tracking;
 	bool			per_pkg;
 	bool			precise_max;
+	bool			overwrite;
 	/* parse modifier helper */
 	int			exclude_GH;
 	int			nr_members;
-- 
1.8.3.4

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