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Date: Fri, 24 Jun 2022 17:41:44 +0200
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Subject: Re: Large interruptions for EAL thread running on isol core
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To: Stephen Hemminger <stephen@networkplumber.org>
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References: <CAO8pfF=yo37Ng5QAcopL=6LgKMHr4+=pPcONPATyS+OD0GLgfg@mail.gmail.com>
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From: Carsten Andrich <carsten.andrich@tu-ilmenau.de>
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I cannot find SCHED_NO_HZ_FULL in v5.18:
https://elixir.bootlin.com/linux/latest/A/ident/SCHED_NO_HZ_FULL

Could you elaborate?

Thanks and best regards,
Carsten

On 24.06.22 17:01, Stephen Hemminger wrote:
> On Thu, 23 Jun 2022 21:03:49 +0200
> Carsten Andrich <carsten.andrich@tu-ilmenau.de> wrote:
>
>>   2. Use real-time priority (SCHED_FIFO w/ priority 99) for the DPDK
>>      threads and
>>      echo -1 > /proc/sys/kernel/sched_rt_runtime_us
>>      to disable the runtime limit. With the runtime limit in place, the
>>      SCHED_FIFO performance will be significantly worse than SCHED_OTHER.
> This can cause major issues if application is normal DPDK application (never does system calls).
> If an interrupt or other event happens on your isolated CPU, the work that it would
> do in soft irq is never performed. FIFO has higher priority than kernel threads.
> This can lead to mystery lockups from other applications (reads not completing, network timeouts, etc).
>
> In any semi-recent kernel using SCHED_NO_HZ_FULL will keep clock ticks from happening
> on the isolated cores.