linux-kernel - Re: [PATCH] sched/fair: reduce false sharing on sched_balance

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Message-ID: <895d688d-64aa-4321-9978-8773e726aee2@linux.ibm.com>
Date: Fri, 25 Apr 2025 21:35:10 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        Sean Christopherson <seanjc@...gle.com>, Josh Don <joshdon@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH] sched/fair: reduce false sharing on sched_balance_running



On 4/23/25 23:16, Eric Dumazet wrote:
> rebalance_domains() can attempt to change sched_balance_running
> more than 350,000 times per second on our servers.
> 
> If sched_clock_irqtime and sched_balance_running share the
> same cache line, we see a very high cost on hosts with 480 threads
> dealing with many interrupts.
> 
> This patch only acquires sched_balance_running when sd->last_balance
> is old enough.
> 
> It also moves sched_balance_running into a dedicated cache line on SMP.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Yafang Shao <laoar.shao@...il.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Josh Don <joshdon@...gle.com>
> ---

Hi Eric.

Please check this thread which does the same thing AFAIU.
https://lore.kernel.org/all/20250416035823.1846307-1-tim.c.chen@linux.intel.com/

You could also try:
https://lore.kernel.org/all/82baaf6c-f3d9-4c3e-be69-24389eadb18c@linux.ibm.com/

Thanks