Re: [BUG] perf_counter: change cpu frequencies

Eric Dumazet
2009-05-03T06:08:17Z

Eric Dumazet a écrit :
> Eric Dumazet a écrit :
>
>> But if I use plain "perf stat -a sleep 10"
>> it seems I get wrong values again (16 G cycles/sec) for all next perf sessions
>>
>
> Well, I confirm all my cpus switched from 3GHz to 2GHz, after
>
> "perf stat -a sleep 10"
>
> (but "perf stat -e instructions -e cycles -a sleep 10" doesnt trigger this problem)
>
> Nothing logged, and /proc/cpuinfo stills reports 3 GHz frequencies
>
> # cat unit.c
> main() {
> int i;
> for (i = 0 ; i < 10000000; i++)
> getppid();
> }
> # time ./unit
>
> real 0m0.818s
> user 0m0.289s
> sys 0m0.529s
> # perf stat -a sleep 10 2>/dev/null
> # time ./unit
>
> real 0m1.122s
> user 0m0.482s
> sys 0m0.640s
>
> # tail -n 27 /proc/cpuinfo
> processor : 7
> vendor_id : GenuineIntel
> cpu family : 6
> model : 23
> model name : Intel(R) Xeon(R) CPU E5450 @ 3.00GHz
> stepping : 6
> cpu MHz : 3000.102
> cache size : 6144 KB
> physical id : 1
> siblings : 1
> core id : 3
> cpu cores : 4
> apicid : 7
> initial apicid : 7
> fdiv_bug : no
> hlt_bug : no
> f00f_bug : no
> coma_bug : no
> fpu : yes
> fpu_exception : yes
> cpuid level : 10
> wp : yes
> flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm constant_tsc arch_perfmon pebs bts pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 lahf_lm tpr_shadow vnmi flexpriority
> bogomips : 6000.01
> clflush size : 64
> power management:
>
> # grep CPU_FREQ .config
> # CONFIG_CPU_FREQ is not set
>
>
> perf_counter seems promising, but still... needs some bug hunting :)
>

Update :

Mike Galbraith suggested me to try various things, and finally, I discovered
this frequency change was probably a BIOS problem on my HP BL460c G1

System Options -> Power regulator for Proliant

[*] HP Dynamic Power Savings Mode
[ ] HP Static Low Power Mode
[ ] HP Static High Performance Mode
[ ] OS Control Mode

I switched it to 'OS Control Mode'

Then acpi-cpufreq could load, and no more frequencies changes on a "perf -a sleep 10"
session, using or not cpufreq.
(Supported cpufreq speeds on these cpus : 1999 & 2999 MHz)

So it was a BIOS issue

# perf stat -a sleep 10

Performance counter stats for 'sleep':

80005.418223 task clock ticks (msecs)
80266 context switches (events)
3 CPU migrations (events)
486 pagefaults (events)
240013851624 CPU cycles (events) << good >>
239076501419 instructions (events)
679464 cache references (events)
<not counted> cache misses

Wall-clock time elapsed: 10000.468808 msecs

Thank you