From: Ingo Molnar <mingo@kernel.org>
To: Valentin Schneider <vschneid@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Shrikanth Hegde <sshegde@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 1/9] sched/balancing: Switch the 'DEFINE_SPINLOCK(balancing)' spinlock into an 'atomic_t sched_balance_running' flag
Date: Fri, 8 Mar 2024 10:48:55 +0100 [thread overview]
Message-ID: <ZerfB+r3XAEKAezy@gmail.com> (raw)
In-Reply-To: <xhsmhh6hldkau.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
* Valentin Schneider <vschneid@redhat.com> wrote:
> On 04/03/24 10:48, Ingo Molnar wrote:
> > The 'balancing' spinlock added in:
> >
> > 08c183f31bdb ("[PATCH] sched: add option to serialize load balancing")
> >
> > ... is taken when the SD_SERIALIZE flag is set in a domain, but in reality it
> > is a glorified global atomic flag serializing the load-balancing of
> > those domains.
> >
> > It doesn't have any explicit locking semantics per se: we just
> > spin_trylock() it.
> >
> > Turn it into a ... global atomic flag. This makes it more
> > clear what is going on here, and reduces overhead and code
> > size a bit:
> >
> > # kernel/sched/fair.o: [x86-64 defconfig]
> >
> > text data bss dec hex filename
> > 60730 2721 104 63555 f843 fair.o.before
> > 60718 2721 104 63543 f837 fair.o.after
> >
> > Also document the flag a bit.
> >
> > No change in functionality intended.
> >
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Vincent Guittot <vincent.guittot@linaro.org>
> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Valentin Schneider <vschneid@redhat.com>
>
> Few comment nits, otherwise:
>
> Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Thanks!
> > -static DEFINE_SPINLOCK(balancing);
> > +/*
> > + * This flag serializes load-balancing passes over large domains
> > + * (such as SD_NUMA) - only once load-balancing instance may run
> ^^^^
> s/once/one/
>
> Also, currently the flag is only set for domains above the NODE topology
> level, sd_init() will reject an architecture that forces SD_SERIALIZE in a
> topology level's ->sd_flags(), so what about:
>
> s/(such as SD_NUMA)/(above the NODE topology level)
Agreed & done.
> > + * at a time, to reduce overhead on very large systems with lots
> > + * of CPUs and large NUMA distances.
> > + *
> > + * - Note that load-balancing passes triggered while another one
> > + * is executing are skipped and not re-tried.
> > + *
> > + * - Also note that this does not serialize sched_balance_domains()
> ^^^^^^^^^^^^^^^^^^^^^
> Did you mean rebalance_domains()?
Correct, a later rename that unifies the nomenclature of all the
rebalancing functions along the sched_balance_*() prefix that I have not
posted yet crept back into this comment block, but obviously this patch
should refer to the current namespace. Fixed.
Thanks,
Ingo
next prev parent reply other threads:[~2024-03-08 9:49 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-04 9:48 [PATCH -v3 0/9] sched/balancing: Misc updates & cleanups Ingo Molnar
2024-03-04 9:48 ` [PATCH 1/9] sched/balancing: Switch the 'DEFINE_SPINLOCK(balancing)' spinlock into an 'atomic_t sched_balance_running' flag Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-08 9:48 ` Ingo Molnar [this message]
2024-03-05 11:11 ` Shrikanth Hegde
2024-03-08 11:23 ` Ingo Molnar
2024-03-08 14:48 ` Shrikanth Hegde
2024-03-12 10:57 ` Ingo Molnar
2024-03-21 12:12 ` Shrikanth Hegde
2024-03-04 9:48 ` [PATCH 2/9] sched/balancing: Remove reliance on 'enum cpu_idle_type' ordering when iterating [CPU_MAX_IDLE_TYPES] arrays in show_schedstat() Ingo Molnar
2024-03-04 15:05 ` Shrikanth Hegde
2024-03-08 9:55 ` Ingo Molnar
2024-03-04 9:48 ` [PATCH 3/9] sched/balancing: Change 'enum cpu_idle_type' to have more natural definitions Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-06 15:46 ` Vincent Guittot
2024-03-08 9:59 ` Ingo Molnar
2024-03-04 9:48 ` [PATCH 4/9] sched/balancing: Change comment formatting to not overlap Git conflict marker lines Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-06 15:44 ` Vincent Guittot
2024-03-04 9:48 ` [PATCH 5/9] sched/balancing: Fix comments (trying to) refer to NOHZ_BALANCE_KICK Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-06 15:43 ` Vincent Guittot
2024-03-08 10:11 ` Ingo Molnar
2024-03-04 9:48 ` [PATCH 6/9] sched/balancing: Update run_rebalance_domains() comments Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-06 16:17 ` Vincent Guittot
2024-03-08 10:15 ` Ingo Molnar
2024-03-08 11:57 ` Vincent Guittot
2024-03-08 16:45 ` Valentin Schneider
2024-03-04 9:48 ` [PATCH 7/9] sched/balancing: Vertically align the comments of 'struct sg_lb_stats' and 'struct sd_lb_stats' Ingo Molnar
2024-03-05 10:50 ` Valentin Schneider
2024-03-04 9:48 ` [PATCH 8/9] sched/balancing: Update comments in " Ingo Molnar
2024-03-05 10:51 ` Valentin Schneider
2024-03-04 9:48 ` [PATCH 9/9] sched/balancing: Rename run_rebalance_domains() => sched_balance_softirq() Ingo Molnar
2024-03-05 10:51 ` Valentin Schneider
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