Commit 7fb4b407 authored by Wang Nan's avatar Wang Nan Committed by Arnaldo Carvalho de Melo

perf mmap: Don't discard prev in backward mode

'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: default avatarWang Nan <wangnan0@huawei.com>
Tested-by: default avatarKan Liang <kan.liang@intel.com>
Acked-by: default avatarNamhyung 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.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 71f566a3
......@@ -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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