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.
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
