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Groups > linux.kernel > #1405125

[PATCH v3 03/11] perf record: Rename variable to make code clear

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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 very intutive. 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 f302cc9..73ce651 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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[PATCH v3 00/11] perf tools: Support overwritable ring buffer Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
  [PATCH v3 11/11] perf tools: Check write_backward during evlist config Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
  [PATCH v3 10/11] perf tools: Don't warn about out of order event if write_backward is used Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
  [PATCH v3 03/11] perf record: Rename variable to make code clear Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
    [tip:perf/urgent] perf record: Rename variable to make code clear tip-bot for Wang Nan <tipbot@zytor.com> - 2016-05-24 07:50 +0200
  [PATCH v3 09/11] perf record: Toggle overwrite ring buffer for reading Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
  [PATCH v3 02/11] perf record: Prevent reading invalid data in record__mmap_read Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
    [tip:perf/urgent] perf record: Prevent reading invalid data in  record__mmap_read tip-bot for Wang Nan <tipbot@zytor.com> - 2016-05-24 07:50 +0200
  [PATCH v3 07/11] perf tools: Enable overwrite settings Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200
  [PATCH v3 08/11] perf record: Introduce rec->overwrite_evlist for overwritable events Wang Nan <wangnan0@huawei.com> - 2016-05-23 09:20 +0200

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