linux-kernel - Re: [RFC PATCH 1/1] sched: Extend cpu idle state for 1ms

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Message-ID: <934429dc-03d7-f7d4-8828-723e756f1411@efficios.com>
Date:   Wed, 26 Jul 2023 15:16:34 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Swapnil Sapkal <Swapnil.Sapkal@....com>,
        Aaron Lu <aaron.lu@...el.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 1/1] sched: Extend cpu idle state for 1ms

On 7/26/23 14:56, Mathieu Desnoyers wrote:
> On 7/26/23 13:40, Shrikanth Hegde wrote:
[...]
>> Do you have SMT here? What is the system utilization when you are running
>> this workload?
> 
> Yes, SMT is enabled, which brings the number of logical cpus to 384.

Here is an additional interesting data point with nosmt=force on
6.4.4:

hackbench -g 32 -f 20 --threads --pipe -l 480000 -s 100

baseline:                       90s
with idle-delay+nr_running<=4:  87s (3% speedup)

hackbench -g 16 -f 20 --threads --pipe -l 480000 -s 100

baseline:                       52s
with idle-delay+nr_running<=4:  32s (38% speedup)

So the impact of the patch appears to depend on how much the
system actually reaches idle, which does make sense.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com