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Subject[PATCH 08/44] perf stat: Improve scaling
Date
From: Andi Kleen <ak@linux.intel.com>

The multiplexing scaling in perf stat mysteriously adds 0.5 to the
value. This dates back to the original perf tool. Other scaling code
doesn't use that strange convention. Remove the extra 0.5.

Before:

$ perf stat -e 'cycles,cycles,cycles,cycles,cycles,cycles' grep -rq foo

Performance counter stats for 'grep -rq foo':

6,403,580 cycles (81.62%)
6,404,341 cycles (81.64%)
6,402,983 cycles (81.62%)
6,399,941 cycles (81.63%)
6,399,451 cycles (81.62%)
6,436,105 cycles (91.87%)

0.005843799 seconds time elapsed

0.002905000 seconds user
0.002902000 seconds sys

After:

$ perf stat -e 'cycles,cycles,cycles,cycles,cycles,cycles' grep -rq foo

Performance counter stats for 'grep -rq foo':

6,422,704 cycles (81.68%)
6,401,842 cycles (81.68%)
6,398,432 cycles (81.68%)
6,397,098 cycles (81.68%)
6,396,074 cycles (81.67%)
6,434,980 cycles (91.62%)

0.005884437 seconds time elapsed

0.003580000 seconds user
0.002356000 seconds sys

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
LPU-Reference: 20190314225002.30108-10-andi@firstfloor.org
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/evsel.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 53ec40cacd4b..16f02b83b23f 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1342,7 +1342,7 @@ void perf_counts_values__scale(struct perf_counts_values *count,
count->val = 0;
} else if (count->run < count->ena) {
scaled = 1;
- count->val = (u64)((double) count->val * count->ena / count->run + 0.5);
+ count->val = (u64)((double) count->val * count->ena / count->run);
}
}

--
2.20.1
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