Re: Random abnormal high CPU sys usage related to timer

[Mac Lin]

Hi Vegard,
Thanks for the prompt response.
The commit is introduced since 4.6, but the issue can be reproduced at
3.10 (earliest I have ever test). And testing on buildroot+4.7 with
the commit reverted, the issue still happen.

In fact, I did a test that ran a script that keep increase a counter
for 10 seconds on the same CPU. If I ran 2 of it, the number is half
of running 1. But if I ran it while the issue happened, the counter
reported is around the same value as the 1 process case. So I doubt
that it might be an issue of reported number.

Is there other way to ensure the CPU is "really" doing something?

x=0
trap 'echo x=$x;exit 1' SIGHUP SIGINT SIGTERM
while : ; do
        x=$(($x+1));
#       echo $x;
done


On Sat, Aug 27, 2016 at 5:12 AM, Vegard Nossum <vegard.nossum@xxxxxxxxx> wrote:
> On 26 August 2016 at 19:10, Mac Lin <mkl0301@xxxxxxxxx> wrote:
>> We were having issue with our userspace application which
>> __sometimes__ result in high CPU sys usage at each execution. The high
>> sys CPU usage persist until the application is killed.
> [...]
>> Googling found one issue that seems related, but no further action.
>
> Was it this one? https://lkml.org/lkml/2016/8/23/360
>
> If so you may try to revert commit ff9a9b4c4334 ("sched, time: Switch
> VIRT_CPU_ACCOUNTING_GEN to jiffy granularity") to see if it helps.
>
>
> Vegard