linux-kernel - Re: [RFC PATCH 0/7] Optimization to reduce the cost of newidle balance

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Message-ID: <ZpdAEYN1vwlnIGiS@chenyu5-mobl2>
Date: Wed, 17 Jul 2024 11:52:49 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Matt Fleming <matt@...dmodwrite.com>
CC: <aaron.lu@...el.com>, <dietmar.eggemann@....com>,
	<gautham.shenoy@....com>, <juri.lelli@...hat.com>, <kprateek.nayak@....com>,
	<linux-kernel@...r.kernel.org>, <mgorman@...hsingularity.net>,
	<mingo@...hat.com>, <peterz@...radead.org>, <tim.c.chen@...el.com>,
	<vincent.guittot@...aro.org>, <yu.chen.surf@...il.com>, <yujie.liu@...el.com>
Subject: Re: [RFC PATCH 0/7] Optimization to reduce the cost of newidle
 balance

Hi Matt,

On 2024-07-16 at 15:16:45 +0100, Matt Fleming wrote:
> > Hi,
> > 
> > This is the second version of the newidle balance optimization[1].
> > It aims to reduce the cost of newidle balance which is found to
> > occupy noticeable CPU cycles on some high-core count systems.
> 
> Hi there, what's the status of this series?
> 

Thanks for your interest in this patch series. The RFC patch series was sent
out to seek for directions and to see if this issue is worthy to fix. Since
you have encountered this issue as well and it seems to be generic issue,
I'll rebase thie patch series and retest it on top of latest kernel and then
send out a new version.

> I'm seeing this same symptom of burning cycles in update_sd_lb_stats() on an
> AMD EPYC 7713 machine (128 CPUs, 8 NUMA nodes). The machine is about 50% idle
> and upadte_sd_lb_stats() sits as the first entry in perf top with about 3.62%
> of CPU cycles.

May I know what benchmark(test scenario) you are testing? I'd like to replicate
this test on my machine as well.

thanks,
Chenyu

> 
> Thanks,
> Matt