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sched/core: Fix arch_scale_freq_tick() on tickless systems 

Bugzilla: https://bugzilla.redhat.com/1996625

commit 7fb3ff22ad8772bbf0e3ce1ef3eb7b09f431807f
Author: Yair Podemsky <ypodemsk@redhat.com>
Date:   Wed Nov 30 14:51:21 2022 +0200

    sched/core: Fix arch_scale_freq_tick() on tickless systems

    In order for the scheduler to be frequency invariant we measure the
    ratio between the maximum CPU frequency and the actual CPU frequency.

    During long tickless periods of time the calculations that keep track
    of that might overflow, in the function scale_freq_tick():

      if (check_shl_overflow(acnt, 2*SCHED_CAPACITY_SHIFT, &acnt))
              goto error;

    eventually forcing the kernel to disable the feature for all CPUs,
    and show the warning message:

       "Scheduler frequency invariance went wobbly, disabling!".

    Let's avoid that by limiting the frequency invariant calculations
    to CPUs with regular tick.

    Fixes: e2b0d619b4 ("x86, sched: check for counters overflow in frequency invariant accounting")
    Suggested-by: "Peter Zijlstra (Intel)" <peterz@infradead.org>
    Signed-off-by: Yair Podemsky <ypodemsk@redhat.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Reviewed-by: Valentin Schneider <vschneid@redhat.com>
    Acked-by: Giovanni Gherdovich <ggherdovich@suse.cz>
    Link: https://lore.kernel.org/r/20221130125121.34407-1-ypodemsk@redhat.com

Signed-off-by: Phil Auld <pauld@redhat.com>
This commit is contained in:
Phil Auld 2023-03-30 11:52:21 -04:00
parent 74288e27bc
commit e59312ac89
1 changed files with 3 additions and 1 deletions
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4
kernel/sched/core.c
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@ -5590,7 +5590,9 @@ void scheduler_tick(void)
unsigned long thermal_pressure;
u64 resched_latency;
arch_scale_freq_tick();
if (housekeeping_cpu(cpu, HK_TYPE_TICK))
arch_scale_freq_tick();
sched_clock_tick();
rq_lock(rq, &rf);