On Tue, Jul 21, 2015 at 02:14:54PM -0400, Vince Weaver wrote:
> I tried to replicate the problem using perf, but for some reason I can't
> get perf to multiplex on any of my machines. That used to transparently
> work didn't it?
>
> here's the result on the haswell machine
>
> perf stat -e
> cycles,instructions,cycles,instructions,cycles,instructions,cycles,instructions
>
> sleep 5
>
> Performance counter stats for 'sleep 5':
>
> 1,354,527 cycles
> 1,934,694 instructions # 1.76 insns per cycle
>
> 1,521,148 cycles
> 1,934,694 instructions # 1.76 insns per cycle
>
> 1,521,148 cycles
> 1,223,321 instructions # 1.11 insns per cycle
> [13.61%]
> <not counted> cycles
> <not counted> instructions
>
> 5.003651781 seconds time elapsed
This is because sleep 5 is idle, and an task that's scheduled-out
doesn't have a rotation timer programmed.
If you use cpu-wide events, or a busy task it works:
# perf stat -ae
cycles,instructions,cycles,instructions,cycles,instructions,cycles,instructions
-- sleep 5
Performance counter stats for 'system wide':
15,460,117,724 cycles
(62.79%)
4,276,675,617 instructions # 0.28 insns per cycle
(62.77%)
15,475,455,605 cycles
(62.75%)
4,284,683,187 instructions # 0.28 insns per cycle
(62.74%)
15,483,305,807 cycles
(62.74%)
4,286,820,811 instructions # 0.28 insns per cycle
(62.63%)
15,410,655,866 cycles
(62.59%)
4,257,624,307 instructions # 0.28 insns per cycle
(62.60%)
5.002916366 seconds time elapsed
# perf stat -e
cycles,instructions,cycles,instructions,cycles,instructions,cycles,instructions
-- ./spin5.sh
Performance counter stats for './spin5.sh':
16,195,427,921 cycles
(62.45%)
35,544,317,856 instructions # 2.20 insns per cycle
(62.43%)
16,181,167,756 cycles
(62.49%)
35,484,446,997 instructions # 2.19 insns per cycle
(62.54%)
16,167,563,501 cycles
(62.58%)
35,486,346,040 instructions # 2.19 insns per cycle
(62.57%)
16,177,845,357 cycles
(62.56%)
35,532,260,091 instructions # 2.20 insns per cycle
(62.48%)
5.009328353 seconds time elapsed
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