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

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Message-ID: <CANn89iLgMFeVz3nwpe1=tf6DbQGi+M9EaUcV=-5-iGQ6QtgxxQ@mail.gmail.com>
Date: Fri, 25 Apr 2025 09:14:31 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.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 Fri, Apr 25, 2025 at 9:05 AM Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:
>
>
>
> 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/

Ah perfect, can we get this merged ?

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