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>

1 files changed, 8 insertions, 0 deletions

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 2b9f898efea6..8847bec64c54 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;