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[PATCH v7 7/8] perf tools: Check write_backward during evlist config

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  [PATCH v7 7/8] perf tools: Check write_backward during evlist config Wang Nan <wangnan0@huawei.com> - 2016-06-15 04:30 +0200
    Re: [PATCH v7 7/8] perf tools: Check write_backward during evlist  config Arnaldo Carvalho de Melo <acme@kernel.org> - 2016-06-16 23:50 +0200
      Re: [PATCH v7 7/8] perf tools: Check write_backward during evlist  config "Wangnan (F)" <wangnan0@huawei.com> - 2016-06-20 06:20 +0200
      [tip:perf/core] perf evsel: Fix write_backwards fallback tip-bot for Arnaldo Carvalho de Melo <tipbot@zytor.com> - 2016-06-22 09:50 +0200

#1422498 — [PATCH v7 7/8] perf tools: Check write_backward during evlist config

Before this patch, when using overwritable ring buffer on an old
kernel, error message is misleading:

 # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
 Error:
 The raw_syscalls:sys_enter event is not supported.

This patch output clear error message to tell user his/her kernel
is too old:

 # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
 Reading from overwrite event is not supported by this kernel
 Error:
 The raw_syscalls:sys_enter event is not supported.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/util/evsel.c  | 17 +++++------------
 tools/perf/util/evsel.h  | 13 +++++++++++++
 tools/perf/util/record.c | 17 +++++++++++++++++
 3 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index ef223c7..59a69bb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -29,17 +29,7 @@
 #include "trace-event.h"
 #include "stat.h"
 
-static struct {
-	bool sample_id_all;
-	bool exclude_guest;
-	bool mmap2;
-	bool cloexec;
-	bool clockid;
-	bool clockid_wrong;
-	bool lbr_flags;
-	bool write_backward;
-} perf_missing_features;
-
+struct perf_missing_features perf_missing_features;
 static clockid_t clockid;
 
 static int perf_evsel__no_extra_init(struct perf_evsel *evsel __maybe_unused)
@@ -690,8 +680,11 @@ static void apply_config_terms(struct perf_evsel *evsel,
 	 * possible to set overwrite globally, without config
 	 * terms.
 	 */
-	if (evsel->overwrite)
+	if (evsel->overwrite) {
+		WARN_ONCE(perf_missing_features.write_backward,
+			  "Reading from overwrite event is not supported by this kernel\n");
 		attr->write_backward = 1;
+	}
 
 	/* User explicitly set per-event callgraph, clear the old setting and reset. */
 	if ((callgraph_buf != NULL) || (dump_size > 0) || max_stack) {
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 55ff958..17e506a 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -11,6 +11,19 @@
 #include "cpumap.h"
 #include "counts.h"
 
+struct perf_missing_features {
+	bool sample_id_all;
+	bool exclude_guest;
+	bool mmap2;
+	bool cloexec;
+	bool clockid;
+	bool clockid_wrong;
+	bool lbr_flags;
+	bool write_backward;
+};
+
+extern struct perf_missing_features perf_missing_features;
+
 struct perf_evsel;
 
 /*
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index 481792c..e3ab812 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -90,6 +90,11 @@ static void perf_probe_context_switch(struct perf_evsel *evsel)
 	evsel->attr.context_switch = 1;
 }
 
+static void perf_probe_write_backward(struct perf_evsel *evsel)
+{
+	evsel->attr.write_backward = 1;
+}
+
 bool perf_can_sample_identifier(void)
 {
 	return perf_probe_api(perf_probe_sample_identifier);
@@ -129,6 +134,17 @@ bool perf_can_record_cpu_wide(void)
 	return true;
 }
 
+static void perf_check_write_backward(void)
+{
+	static bool checked = false;
+
+	if (!checked) {
+		perf_missing_features.write_backward =
+			!perf_probe_api(perf_probe_write_backward);
+		checked = true;
+	}
+}
+
 void perf_evlist__config(struct perf_evlist *evlist, struct record_opts *opts,
 			 struct callchain_param *callchain)
 {
@@ -136,6 +152,7 @@ void perf_evlist__config(struct perf_evlist *evlist, struct record_opts *opts,
 	bool use_sample_identifier = false;
 	bool use_comm_exec;
 
+	perf_check_write_backward();
 	/*
 	 * Set the evsel leader links before we configure attributes,
 	 * since some might depend on this info.
-- 
1.8.3.4

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#1424467 — Re: [PATCH v7 7/8] perf tools: Check write_backward during evlist config

Em Wed, Jun 15, 2016 at 02:23:34AM +0000, Wang Nan escreveu:
> Before this patch, when using overwritable ring buffer on an old
> kernel, error message is misleading:
> 
>  # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
>  Error:
>  The raw_syscalls:sys_enter event is not supported.
> 
> This patch output clear error message to tell user his/her kernel
> is too old:
> 
>  # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
>  Reading from overwrite event is not supported by this kernel
>  Error:
>  The raw_syscalls:sys_enter event is not supported.

So I went to see if exposing that missing_features struct outside
evsel.c was strictly needed and found that we already have fallbacking
for this feature (attr.write_backwards) i.e. if we set it and
sys_perf_event_open() fails, we will check if we are asking the kernel
for some attr. field that it doesn't supports, set that missing_features
and try again.

But the way this was done for attr.write_backwards was buggy, as we need
to check features in the inverse order of their introduction to the
kernel, so that a newer tool checks first the newest perf_event_attr
fields, detecting that the older kernel doesn't have support for them.
The patch that introduced write_backwards support ([1]) in perf_evsel__open()
did this checking after all the other older attributes, wrongly.

[1]: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward")

Also we shouldn't even try to call sys_perf_event_open if
perf_missing_features.write_backward is true and evsel->overwrite is
also true, the old code would check this only after successfully opening
the fd, do it before the open loop.

Please take a look at the following patch, see if it is sufficient for
handling older kernels, probably we need to emit a message to the user,
but that has to be done at the builtin- level, i.e. at the tool, i.e.
perf_evsel_open__strerror() should have what it takes to figure out this
extra error and provide/ a proper string, lemme add this to the patch...
done, please check:

write_backwards_fallback.patch:

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9b2e3e624efe..4e8e6d8795d0 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1389,8 +1389,11 @@ fallback_missing_features:
 	if (perf_missing_features.lbr_flags)
 		evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
 				     PERF_SAMPLE_BRANCH_NO_CYCLES);
-	if (perf_missing_features.write_backward)
+	if (perf_missing_features.write_backward) {
+		if (evsel->overwrite)
+			return -EINVAL;
 		evsel->attr.write_backward = false;
+	}
 retry_sample_id:
 	if (perf_missing_features.sample_id_all)
 		evsel->attr.sample_id_all = 0;
@@ -1453,12 +1456,6 @@ retry_open:
 				err = -EINVAL;
 				goto out_close;
 			}
-
-			if (evsel->overwrite &&
-			    perf_missing_features.write_backward) {
-				err = -EINVAL;
-				goto out_close;
-			}
 		}
 	}
 
@@ -1496,7 +1493,10 @@ try_fallback:
 	 * Must probe features in the order they were added to the
 	 * perf_event_attr interface.
 	 */
-	if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
+	if (!perf_missing_features.write_backward && evsel->attr.write_backward) {
+		perf_missing_features.write_backward = true;
+		goto fallback_missing_features;
+	} else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
 		perf_missing_features.clockid_wrong = true;
 		goto fallback_missing_features;
 	} else if (!perf_missing_features.clockid && evsel->attr.use_clockid) {
@@ -1521,10 +1521,6 @@ try_fallback:
 			  PERF_SAMPLE_BRANCH_NO_FLAGS))) {
 		perf_missing_features.lbr_flags = true;
 		goto fallback_missing_features;
-	} else if (!perf_missing_features.write_backward &&
-			evsel->attr.write_backward) {
-		perf_missing_features.write_backward = true;
-		goto fallback_missing_features;
 	}
 
 out_close:
@@ -2409,6 +2405,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 	"We found oprofile daemon running, please stop it and try again.");
 		break;
 	case EINVAL:
+		if (evsel->overwrite && perf_missing_features.write_backward)
+			return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel.");
 		if (perf_missing_features.clockid)
 			return scnprintf(msg, size, "clockid feature not supported.");
 		if (perf_missing_features.clockid_wrong)

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#1426180 — Re: [PATCH v7 7/8] perf tools: Check write_backward during evlist config

On 2016/6/17 5:47, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 15, 2016 at 02:23:34AM +0000, Wang Nan escreveu:
>> Before this patch, when using overwritable ring buffer on an old
>> kernel, error message is misleading:
>>
>>   # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
>>   Error:
>>   The raw_syscalls:sys_enter event is not supported.
>>
>> This patch output clear error message to tell user his/her kernel
>> is too old:
>>
>>   # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
>>   Reading from overwrite event is not supported by this kernel
>>   Error:
>>   The raw_syscalls:sys_enter event is not supported.
> So I went to see if exposing that missing_features struct outside
> evsel.c was strictly needed and found that we already have fallbacking
> for this feature (attr.write_backwards) i.e. if we set it and
> sys_perf_event_open() fails, we will check if we are asking the kernel
> for some attr. field that it doesn't supports, set that missing_features
> and try again.
>
> But the way this was done for attr.write_backwards was buggy, as we need
> to check features in the inverse order of their introduction to the
> kernel, so that a newer tool checks first the newest perf_event_attr
> fields, detecting that the older kernel doesn't have support for them.
> The patch that introduced write_backwards support ([1]) in perf_evsel__open()
> did this checking after all the other older attributes, wrongly.
>
> [1]: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward")
>
> Also we shouldn't even try to call sys_perf_event_open if
> perf_missing_features.write_backward is true and evsel->overwrite is
> also true, the old code would check this only after successfully opening
> the fd, do it before the open loop.
>
> Please take a look at the following patch, see if it is sufficient for
> handling older kernels, probably we need to emit a message to the user,
> but that has to be done at the builtin- level, i.e. at the tool, i.e.
> perf_evsel_open__strerror() should have what it takes to figure out this
> extra error and provide/ a proper string, lemme add this to the patch...
> done, please check:
>
> write_backwards_fallback.patch:

[SNIP]

>   
> @@ -1496,7 +1493,10 @@ try_fallback:
>   	 * Must probe features in the order they were added to the
>   	 * perf_event_attr interface.
>   	 */

I read this comment but misunderstand. I thought 'order' means newest last.

Will try your patch. Thank you.

> -	if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
> +	if (!perf_missing_features.write_backward && evsel->attr.write_backward) {
> +		perf_missing_features.write_backward = true;
> +		goto fallback_missing_features;
> +	} else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
>   		perf_missing_features.clockid_wrong = true;
>   		goto fallback_missing_features;
>   	} else if (!perf_missing_features.clockid && evsel->attr.use_clockid) {
> @@ -1521,10 +1521,6 @@ try_fallback:
>   			  PERF_SAMPLE_BRANCH_NO_FLAGS))) {
>   		perf_missing_features.lbr_flags = true;
>   		goto fallback_missing_features;
> -	} else if (!perf_missing_features.write_backward &&
> -			evsel->attr.write_backward) {
> -		perf_missing_features.write_backward = true;
> -		goto fallback_missing_features;
>   	}
>   
>   out_close:
> @@ -2409,6 +2405,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
>   	"We found oprofile daemon running, please stop it and try again.");
>   		break;
>   	case EINVAL:
> +		if (evsel->overwrite && perf_missing_features.write_backward)
> +			return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel.");
>   		if (perf_missing_features.clockid)
>   			return scnprintf(msg, size, "clockid feature not supported.");
>   		if (perf_missing_features.clockid_wrong)

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#1428514 — [tip:perf/core] perf evsel: Fix write_backwards fallback

Commit-ID:  7da36e94e7fad768ca8640b61ed1f49b284e1dc5
Gitweb:     http://git.kernel.org/tip/7da36e94e7fad768ca8640b61ed1f49b284e1dc5
Author:     Arnaldo Carvalho de Melo <acme@kernel.org>
AuthorDate: Mon, 20 Jun 2016 10:47:18 +0000
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 21 Jun 2016 13:18:35 -0300

perf evsel: Fix write_backwards fallback

Commit b90dc17a5d14 "perf evsel: Add overwrite attribute and check
write_backward" misunderstood the 'order' should be obeyed in
__perf_evsel__open.

But the way this was done for attr.write_backwards was buggy, as we need
to check features in the inverse order of their introduction to the
kernel, so that a newer tool checks first the newest perf_event_attr
fields, detecting that the older kernel doesn't have support for them.

Also, we can avoid calling sys_perf_event_open() if we have already
detected the missing of write_backward.

Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Fixes: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward")
Link: http://lkml.kernel.org/r/1466419645-75551-2-git-send-email-wangnan0@huawei.com
Link: http://lkml.kernel.org/r/20160616214724.GI13337@kernel.org
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/evsel.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9b2e3e6..1d8f2bb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1389,8 +1389,11 @@ fallback_missing_features:
 	if (perf_missing_features.lbr_flags)
 		evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
 				     PERF_SAMPLE_BRANCH_NO_CYCLES);
-	if (perf_missing_features.write_backward)
+	if (perf_missing_features.write_backward) {
+		if (evsel->overwrite)
+			return -EINVAL;
 		evsel->attr.write_backward = false;
+	}
 retry_sample_id:
 	if (perf_missing_features.sample_id_all)
 		evsel->attr.sample_id_all = 0;
@@ -1453,12 +1456,6 @@ retry_open:
 				err = -EINVAL;
 				goto out_close;
 			}
-
-			if (evsel->overwrite &&
-			    perf_missing_features.write_backward) {
-				err = -EINVAL;
-				goto out_close;
-			}
 		}
 	}
 
@@ -1496,7 +1493,10 @@ try_fallback:
 	 * Must probe features in the order they were added to the
 	 * perf_event_attr interface.
 	 */
-	if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
+	if (!perf_missing_features.write_backward && evsel->attr.write_backward) {
+		perf_missing_features.write_backward = true;
+		goto fallback_missing_features;
+	} else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
 		perf_missing_features.clockid_wrong = true;
 		goto fallback_missing_features;
 	} else if (!perf_missing_features.clockid && evsel->attr.use_clockid) {
@@ -1521,12 +1521,7 @@ try_fallback:
 			  PERF_SAMPLE_BRANCH_NO_FLAGS))) {
 		perf_missing_features.lbr_flags = true;
 		goto fallback_missing_features;
-	} else if (!perf_missing_features.write_backward &&
-			evsel->attr.write_backward) {
-		perf_missing_features.write_backward = true;
-		goto fallback_missing_features;
 	}
-
 out_close:
 	do {
 		while (--thread >= 0) {
@@ -2409,6 +2404,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 	"We found oprofile daemon running, please stop it and try again.");
 		break;
 	case EINVAL:
+		if (evsel->overwrite && perf_missing_features.write_backward)
+			return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel.");
 		if (perf_missing_features.clockid)
 			return scnprintf(msg, size, "clockid feature not supported.");
 		if (perf_missing_features.clockid_wrong)

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