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Subject[PATCH] perf: Fix performance issue with perf report

On a large machine we spend a lot of time in perf_header__find_attr when
running perf report.

If we are parsing a file without PERF_SAMPLE_ID then for each sample we call
perf_header__find_attr and loop through all counter IDs, never finding a match.
As the machine gets larger there are more per cpu counters and we spend an
awful lot of time in there.

The patch below initialises each sample id to -1ULL and checks for this in
perf_header__find_attr. We may need to do something more intelligent eventually
(eg a hash lookup from counter id to attr) but this at least fixes the most
common usage of perf report.

Signed-off-by: Anton Blanchard <anton@samba.org>
--

Index: linux.trees.git/tools/perf/util/event.c
===================================================================
--- linux.trees.git.orig/tools/perf/util/event.c 2010-05-03 20:20:54.000000000 +1000
+++ linux.trees.git/tools/perf/util/event.c 2010-05-04 21:15:20.000000000 +1000
@@ -713,6 +713,7 @@ int event__parse_sample(event_t *event,
array++;
}

+ data->id = -1ULL;
if (type & PERF_SAMPLE_ID) {
data->id = *array;
array++;
Index: linux.trees.git/tools/perf/util/header.c
===================================================================
--- linux.trees.git.orig/tools/perf/util/header.c 2010-05-03 20:20:54.000000000 +1000
+++ linux.trees.git/tools/perf/util/header.c 2010-05-04 21:15:20.000000000 +1000
@@ -923,6 +923,14 @@ perf_header__find_attr(u64 id, struct pe
{
int i;

+ /*
+ * We set id to -1 if the data file doesn't contain sample
+ * ids. Check for this and avoid walking through the entire
+ * list of ids which may be large.
+ */
+ if (id == -1ULL)
+ return NULL;
+
for (i = 0; i < header->attrs; i++) {
struct perf_header_attr *attr = header->attr[i];
int j;

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