Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1611922
| From | Rik van Riel <riel@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [BUG nohz]: wrong user and system time accounting |
| Date | 2017-03-29 15:20 +0200 |
| Message-ID | <tqlG1-7mo-11@gated-at.bofh.it> (permalink) |
| References | <tohZT-7Mb-5@gated-at.bofh.it> <tqlwl-7hB-9@gated-at.bofh.it> |
| Organization | Red Hat, Inc. |
On Wed, 2017-03-29 at 15:04 +0200, Frederic Weisbecker wrote:
> On Thu, Mar 23, 2017 at 04:55:12PM -0400, Luiz Capitulino wrote:
> >
> > When there are two or more tasks executing in user-space and
> > taking 100% of a nohz_full CPU, top reports 70% system time
> > and 30% user time utilization. Sometimes I'm even able to get
> > 100% system time and 0% user time.
> >
> > This was reproduced with latest Linus tree (093b995), but I
> > don't believe it's a regression (at least not a recent one)
> > as I can reproduce it with older kernels. Also, I have
> > CONFIG_IRQ_TIME_ACCOUNTING=y and haven't tried to reproduce
> > without it yet.
> >
> > Below you'll find the steps to reproduce and some initial
> > analysis.
> >
> > Steps to reproduce
> > ------------------
> >
> > 1. Set up a CPU for nohz_full with isolcpus= nohz_full=
> >
> > 2. Pin two tasks that hog the CPU 100% of the time to that CPU
>
> I failed to reproduce with your config. I'm still getting 99%
> userspace
> cputime. So I'm wondering if the hogging style plays a role.
>
> I run pure user loops:
>
> int main(int argc, char **argv)
> {
> for (;;);
> return 0
> }
>
> Does your user program perform syscalls or IOs of some sort?
Luiz's program makes a syscall every millisecond,
if started with the arguments he gave as his
reproducer.
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Re: [BUG nohz]: wrong user and system time accounting Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-29 15:10 +0200
Re: [BUG nohz]: wrong user and system time accounting Rik van Riel <riel@redhat.com> - 2017-03-29 15:20 +0200
Re: [BUG nohz]: wrong user and system time accounting Luiz Capitulino <lcapitulino@redhat.com> - 2017-03-29 15:30 +0200
Re: [BUG nohz]: wrong user and system time accounting Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-29 23:20 +0200
Re: [BUG nohz]: wrong user and system time accounting Luiz Capitulino <lcapitulino@redhat.com> - 2017-03-30 03:50 +0200
csiph-web