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Subject[tip:perf/core] perf: Fix performance issue with perf report
Commit-ID:  02bf60aad7d5912dfcdbe0154f1bd67ea7a8301e
Gitweb: http://git.kernel.org/tip/02bf60aad7d5912dfcdbe0154f1bd67ea7a8301e
Author: Anton Blanchard <anton@samba.org>
AuthorDate: Tue, 4 May 2010 21:19:15 +1000
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 4 May 2010 10:54:09 -0300

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.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric B Munson <ebmunson@us.ibm.com>
Acked-by: Eric B Munson <ebmunson@us.ibm.com>
LKML-Reference: <20100504111915.GB14636@kryten>
Signed-off-by: Anton Blanchard <anton@samba.org>
--
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/event.c | 1 +
tools/perf/util/header.c | 8 ++++++++
2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 1757b0f..2477270 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -713,6 +713,7 @@ int event__parse_sample(event_t *event, u64 type, struct sample_data *data)
array++;
}

+ data->id = -1ULL;
if (type & PERF_SAMPLE_ID) {
data->id = *array;
array++;
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 2b9f898..8847bec 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -922,6 +922,14 @@ perf_header__find_attr(u64 id, struct perf_header *header)
{
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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