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From: Ingo Molnar <mingo@kernel.org>
To: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Valentin Schneider <vschneid@redhat.com>
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 12:23:10 +0100	[thread overview]
Message-ID: <Zer1Hkxh/UMxs3xs@gmail.com> (raw)
In-Reply-To: <bf612672-f7c3-4585-ac31-e02a1ebf614c@linux.ibm.com>


* Shrikanth Hegde <sshegde@linux.ibm.com> wrote:

> system is at 75% load		<-- 	25.6% contention
> 113K probe:rebalance_domains_L37
> 84K probe:rebalance_domains_L55
> 
> 87
> system is at 100% load		<--	87.5% contention.
> 64K probe:rebalance_domains_L37
> 8K probe:rebalance_domains_L55
> 
> 
> A few reasons for contentions could be: 
>
> 1. idle load balance is running and some other cpu is becoming idle, and 
>    tries newidle_balance.
>
> 2. when system is busy, every CPU would do busy balancing, it would 
>    contend for the lock. It will not do balance as should_we_balance says 
>    this CPU need not balance. It bails out and release the lock.

Thanks, these measurements are really useful!

Would it be possible to disambiguate these two cases?

I think we should probably do something about this contention on this large 
system: especially if #2 'no work to be done' bailout is the common case.

Thanks,

	Ingo

  reply	other threads:[~2024-03-08 11:23 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
2024-03-05 11:11   ` Shrikanth Hegde
2024-03-08 11:23     ` Ingo Molnar [this message]
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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