linux-kernel - Re: [PATCH v3 0/5] Scan for an idle sibling in a single pass

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Message-ID: <20210125114623.GY3592@techsingularity.net>
Date:   Mon, 25 Jan 2021 11:46:23 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Qais Yousef <qais.yousef@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/5] Scan for an idle sibling in a single pass

On Mon, Jan 25, 2021 at 07:37:55PM +0800, Li, Aubrey wrote:
> > It's interesting that patch 3 would make any difference on x64 given that
> > it's SMT2. The scan depth should have been similar. It's somewhat expected
> > that it will not be a universal win, particularly once the utilisation
> > is high enough to spill over in sched domains (25%, 50%, 75% utilisation
> > being interesting on 4-socket systems). In such cases, double scanning can
> > still show improvements for workloads that idle rapidly like tbench and
> > hackbench even though it's expensive. The extra scanning gives more time
> > for a CPU to go idle enough to be selected which can improve throughput
> > but at the cost of wake-up latency,
> 
> aha, sorry for the confusion. Since you and Vincent discussed to drop
> patch3, I just mentioned I tested 5 patches with patch3, not patch3 alone.
> 

Ah, that makes more sense.

> > 
> > Hopefully v4 can be tested as well which is now just a single scan.
> > 
> 
> Sure, may I know the baseline of v4?
> 

5.11-rc4.

-- 
Mel Gorman
SUSE Labs