On Thu, Sep 30, 2021 at 5:22 AM Pierre FICHEUX <pierre.ficheux@xxxxxxxx> wrote:
>
> Hi,
>
> Thx a lot for your help (I suspected such a thing).
>
> I can see CONFIG_CPU_IDLE=y in the config but as it's an old kernel
> (3.10) there is no entry such as
> /sys/devices/system/cpu/cpu?/cpuidle/state?/disable
>
> Will take a look further.
You probably have tuned installed in your system. If so, you could run:
tuned-adm profile realtime
That should set most of the required and suggested configurations, including
the ones Punit wisely mentioned.
Best regards,
Luis
>
> regards
>
> Le jeu. 30 sept. 2021 à 02:13, Punit Agrawal <punitagrawal@xxxxxxxxx> a écrit :
> >
> > Pierre FICHEUX <pierre.ficheux@xxxxxxxx> writes:
> >
> > > Hi,
> > >
> > > I have a strange problem on a PREEMPT_RT system.
> > >
> > > I have a process with 2 threads,
> > >
> > > - 1 TR thread (10 ms period) which places 350 KB blocks in a fifo (1
> > > block every 10 ms).
> > > - 1 non-TR thread (SCHED_OTHER) which reads the block in the fifo and
> > > writes it to the disk
> > >
> > > If I run this on a powerful machine (HP Z4-i9, 14 cores, NVME disk,
> > > CentOS 7 with 3.10 PREEMPT_RT kernel, yes that's ooold), the max
> > > jitter WITH hackbench remains around 20 to 30 µs while the max jitter
> > > WITHOUT hackbench goes up to 350 µs!
> > >
> > > -> hackbench -p -g 20 -l 10000000
> > >
> > > Running the program with taskset 01 doesn't change anything
> > > If I don't write the data to disk it doesn't change anything either.
> > >
> > > The important jitters appear rather at the beginning (but sometimes also later).
> > >
> > > Any ideas ?
> >
> > Is power management (cpuidle, cpufreq) enabled on the system?
> >
> > One possible explanation -
> >
> > The load from the 10ms task, isn't high enough to keep the system at
> > high-frequencies or prevent it from going into deeper sleep states. Both
> > of these can impact latencies.
> >
> > With hackbench, the system is sufficiently busy to avoid the going into
> > idle.
> >
> > >
> > >
> > > thanks by advance
> > >
> > > --
> > > Pierre
>
>
>
> --
>
> Pierre FICHEUX -/- CTO Smile ECS, France -\- pierre.ficheux@xxxxxxxx
> http://www.smile.fr
> https://smile.eu/fr/offres/embarque-iot
> I would love to change the world, but they won't give me the source code
>
