perf mmap: Don't discard prev in backward mode (7fb4b407) · Commits · 戴 / test

'perf record' can switch its output data file. The new output should only store the data after switching. However, in overwrite backward mode, the new output still can have data from before switching. That also brings extra overhead. At the end of mmap_read(), the position of the processed ring buffer is saved in md->prev. Next mmap_read should be end in md->prev if it is not overwriten. That avoids processing duplicate data. However, md->prev is discarded. So next the mmap_read() has to process whole valid ring buffer, which probably includes old processed data. Avoid calling backward_rb_find_range() when md->prev is still available. Signed-off-by:

Wang Nan <wangnan0@huawei.com> Tested-by:

Kan Liang <kan.liang@intel.com> Acked-by:

Namhyung Kim <namhyung@kernel.org> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Mengting Zhang <zhangmengting@huawei.com> Link: http://lkml.kernel.org/r/20171204165107.95327-3-wangnan0@huawei.com Signed-off-by:

Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/mmap.c

+15 −18

Original line number	Diff line number	Diff line
		@@ -267,18 +267,6 @@ static int backward_rb_find_range(void buf, int mask, u64 head, u64 start, u64
		return -1;
		}

		static int rb_find_range(void *data, int mask, u64 head, u64 old,
		u64 start, u64 end, bool backward)
		{
		if (!backward) {
		*start = old;
		*end = head;
		return 0;
		}

		return backward_rb_find_range(data, mask, head, start, end);
		}

		int perf_mmap__push(struct perf_mmap *md, bool backward,
		void to, int push(void to, void *buf, size_t size))
		{
		@@ -290,14 +278,15 @@ int perf_mmap__push(struct perf_mmap *md, bool backward,
		void *buf;
		int rc = 0;

		if (rb_find_range(data, md->mask, head, old, &start, &end, backward))
		return -1;
		start = backward ? head : old;
		end = backward ? old : head;

		if (start == end)
		return 0;

		size = end - start;
		if (size > (unsigned long)(md->mask) + 1) {
		if (!backward) {
		WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");

		md->prev = head;
		@@ -305,6 +294,14 @@ int perf_mmap__push(struct perf_mmap *md, bool backward,
		return 0;
		}

		/*
		* Backward ring buffer is full. We still have a chance to read
		* most of data from it.
		*/
		if (backward_rb_find_range(data, md->mask, head, &start, &end))
		return -1;
		}

		if ((start & md->mask) + size != (end & md->mask)) {
		buf = &data[start & md->mask];
		size = md->mask + 1 - (start & md->mask);

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