Re: [RFC PATCH v5] sched: Fix performance regression introduced by mm_cid

[Aaron Lu]

On Thu, Apr 13, 2023 at 11:11:14AM -0400, Mathieu Desnoyers wrote:
> On 2023-04-13 10:37, Aaron Lu wrote:
> > On Thu, Apr 13, 2023 at 10:02:48AM -0400, Mathieu Desnoyers wrote:
> > > Introduce per-mm/cpu current concurrency id (mm_cid) to fix a PostgreSQL
> > > sysbench regression reported by Aaron Lu.
> > Initial test using postgres_sysbench showed the lock contention is gone :-)
> > Will check how it affects hackbench tomorrow.
> 
> That's good news! Not unexpected though.
> 
> One thing to look closely at is whether it's just that the qspinlocks are
> gone from the profiles but replaced by time spent in __mm_cid_get() due to
> cache-line bouncing of find-first-zero/test-and-set on the per-mm cid
> bitmap.

Found the below two appeared in profile when using cid as keyword, full
profile attached for your reference.

# Children      Self  Shared Object    Symbol
     0.97%     0.62%  [kernel.vmlinux] [k] sched_mm_cid_migrate_from
     0.48%     0.47%  [kernel.vmlinux] [k] mm_cid_get

Thanks,
Aaron

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