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SubjectRe: [RFC 2/2] perf stat: Fix shadow stats for clock events
On Thu, Nov 15, 2018 at 03:25:33PM +0530, Ravi Bangoria wrote:
> Commit 0aa802a79469 ("perf stat: Get rid of extra clock display
> function") introduced scale and unit for clock events. Thus,
> perf_stat__update_shadow_stats() now saves scaled values of
> clock events in msecs, instead of original nsecs. But while
> calculating values of shadow stats we still consider clock
> event values in nsecs. This results in a wrong shadow stat
> values. Ex,
>
> # ./perf stat -e task-clock,cycles ls
> <SNIP>
> 2.62 msec task-clock:u # 0.624 CPUs utilized
> 2,501,536 cycles:u # 1250768.000 GHz
>
> Fix this by considering clock events's saved stats in msecs:
>
> # ./perf stat -e task-clock,cycles ls
> <SNIP>
> 2.42 msec task-clock:u # 0.754 CPUs utilized
> 2,338,747 cycles:u # 1.169 GHz
>
> Note:
> The problem with this approach is, we are losing fractional part
> while converting nsecs to msecs. This results in a sightly different
> values of shadow stats.

yea, could we just leave the NSEC instead? like below

jirka


---
diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index f4bad808bdd9..da8857df238e 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -209,11 +209,12 @@ void perf_stat__update_shadow_stats(struct perf_evsel *counter, u64 count,
int cpu, struct runtime_stat *st)
{
int ctx = evsel_context(counter);
+ u64 count_ns = count;

count *= counter->scale;

if (perf_evsel__is_clock(counter))
- update_runtime_stat(st, STAT_NSECS, 0, cpu, count);
+ update_runtime_stat(st, STAT_NSECS, 0, cpu, count_ns);
else if (perf_evsel__match(counter, HARDWARE, HW_CPU_CYCLES))
update_runtime_stat(st, STAT_CYCLES, ctx, cpu, count);
else if (perf_stat_evsel__is(counter, CYCLES_IN_TX))
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