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SubjectRe: perf stat stddev reporting broken since "perf stat: Introduce read_counters function"
On Mon, Jan 18, 2016 at 05:59:46PM +0000, Mel Gorman wrote:
> I noticed that perf stat in 4.4 is not printing stddev figures as
> expected and bisected it to commit 106a94a0f8c2 ("perf stat: Introduce
> read_counters function").
>
> # Kernel 4.4
> # make clean && make prefix=/usr && ./perf stat -r 5 sleep 1
> Performance counter stats for 'sleep 1' (5 runs):
>
> 0.466683 task-clock (msec) # 0.000 CPUs utilized
> 1 context-switches # 0.002 M/sec
> 1 cpu-migrations # 0.002 M/sec
> 66 page-faults # 0.144 M/sec
> 1,630,220 cycles # 3.562 GHz
> <not supported> stalled-cycles-frontend
> <not supported> stalled-cycles-backend
> 902,686 instructions # 0.66 insns per cycle
> 185,692 branches # 405.786 M/sec
> 8,640 branch-misses # 4.63% of all branches
>
> 1.000855883 seconds time elapsed ( +- 0.01% )
>
> # git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7^
> Performance counter stats for 'sleep 1' (5 runs):
>
> 0.397939 task-clock (msec) # 0.000 CPUs utilized ( +- 3.37% )
> 1 context-switches # 0.003 M/sec
> 0 cpu-migrations # 0.000 K/sec
> 67 page-faults # 0.169 M/sec ( +- 0.56% )
> 1,360,763 cycles # 3.420 GHz ( +- 2.14% )
> <not supported> stalled-cycles-frontend
> <not supported> stalled-cycles-backend
> 903,901 instructions # 0.66 insns per cycle ( +- 0.24% )
> 186,472 branches # 468.595 M/sec ( +- 0.29% )
> 8,599 branch-misses # 4.61% of all branches ( +- 0.77% )
>
> 1.000761882 seconds time elapsed ( +- 0.00% )
>
> # git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7
>
> Performance counter stats for 'sleep 1' (5 runs):
>
> 0.583178 task-clock (msec) # 0.001 CPUs utilized
> 1 context-switches # 0.002 M/sec
> 0 cpu-migrations # 0.000 K/sec
> 67 page-faults # 0.141 M/sec
> 1,224,416 cycles # 2.585 GHz
> <not supported> stalled-cycles-frontend
> <not supported> stalled-cycles-backend
> 892,568 instructions # 0.68 insns per cycle
> 184,975 branches # 390.554 M/sec
> 8,512 branch-misses # 4.57% of all branches
>
> 1.000889249 seconds time elapsed ( +- 0.01% )
>
> I checked and current master in Linus' tree is also broken. Is this
> change in documented perf stat behaviour intentional?

nope, not intentional.. I'll check on that, thanks for reporting

jirka

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