Messages in this thread | | | Date | Fri, 30 Nov 2018 11:21:54 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf evsel: Correct clock unit to nanosecond |
| |
On Fri, Nov 30, 2018 at 06:06:05PM +0800, Leo Yan wrote: > Since commit 0aa802a79469 ("perf stat: Get rid of extra clock display > function"), the cpu and task clock unit has been changed from > nanosecond value to millisecond value. This introduces confusion for > CPU run time statistics, we can see in below flow the clock value is > scaled from nanosecond value to millisecond value; but this is > contradiction with statistics type 'STAT_NSECS', which always takes > clock as nanosecond unit. > > perf_stat__update_shadow_stats() > `-> count *= counter->scale; > update_runtime_stat(st, STAT_NSECS, 0, cpu, count); > > And when 'perf stat' calculates frequencies for cpu cycles and other > events, it uses event count to divide clock and it expects divisor unit > has nanosecond value, but actually the clock value has been scaled to > millisecond value. At the end we can exaggerate values in below output > result (e.g. 500M/sec for context-switches, cycle is 1079636.500 GHz). > > # perf stat -- sleep 1 > > Performance counter stats for 'sleep 1': > > 2.29 msec task-clock # 0.002 CPUs utilized > 1 context-switches # 500.000 M/sec > 1 cpu-migrations # 500.000 M/sec > 53 page-faults # 26500.000 M/sec > 2,159,273 cycles # 1079636.500 GHz > 1,281,566 instructions # 0.59 insn per cycle > 171,153 branches # 85576500.000 M/sec > 17,870 branch-misses # 10.44% of all branches > > To fix this issue, this patch changes back clock unit to nanosecond > level, as result we can see the correct frequency calculation: > > # perf stat -- sleep 1 > > Performance counter stats for 'sleep 1': > > 2,461,180 nsec task-clock # 0.002 CPUs utilized > 1 context-switches # 0.406 K/sec > 0 cpu-migrations # 0.000 K/sec > 54 page-faults # 0.022 M/sec > 2,320,634 cycles # 0.943 GHz > 1,284,442 instructions # 0.55 insn per cycle > 171,425 branches # 69.652 M/sec > 17,970 branch-misses # 10.48% of all branches > > This patch has side effect for changing unit field for perf command. > This is tested with below two cases: one is for normal output format and > another is for cvs output format. > > Before: > > # perf stat -e cpu-clock,task-clock -C 0 sleep 3 > > Performance counter stats for 'CPU(s) 0': > > 3,003.50 msec cpu-clock # 1.000 CPUs utilized > 3,003.50 msec task-clock # 1.000 CPUs utilized > > 3.003697880 seconds time elapsed > > Now: > > # perf stat -e cpu-clock,task-clock -C 0 sleep 3 > > Performance counter stats for 'CPU(s) 0': > > 3,003,684,880 nsec cpu-clock # 1.000 CPUs utilized > 3,003,682,780 nsec task-clock # 1.000 CPUs utilized > > 3.003881982 seconds time elapsed > > Before: > > # perf stat -e cpu-clock,task-clock -C 0 -x, sleep 3 > 3003.64,msec,cpu-clock,3003644320,100.00,1.000,CPUs utilized > 3003.64,msec,task-clock,3003643300,100.00,1.000,CPUs utilized > > Now: > > # perf stat -e cpu-clock,task-clock -C 0 -x, sleep 3 > 3003501460,nsec,cpu-clock,3003501660,100.00,1.000,CPUs utilized > 3003499500,nsec,task-clock,3003499500,100.00,1.000,CPUs utilized > > Cc: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
there was fix for this recently, could you please check if it's working for you: 6e269c85dcea perf stat: Fix shadow stats for clock events
thanks, jirka
| |