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: e2b0d619b400 ("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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25b582b6ee5f78949d7646b2c23f0c4ba593a5d6..965d813c28ad7965c05c39f1a7da4af103bbab2a 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5504,7 +5504,9 @@ 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);