linux-kernel - Re: [PATCH] sched/fair: Consider cpu affinity when allowing NUMA imbalance in find_idlest

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Date:   Wed, 9 Feb 2022 16:47:28 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     aubrey.li@...ux.intel.com, efault@....de, gautham.shenoy@....com,
        linux-kernel@...r.kernel.org, mgorman@...hsingularity.net,
        mingo@...nel.org, song.bao.hua@...ilicon.com,
        srikar@...ux.vnet.ibm.com, valentin.schneider@....com,
        vincent.guittot@...aro.org
Subject: Re: [PATCH] sched/fair: Consider cpu affinity when allowing NUMA
 imbalance in find_idlest_group

Hello Peter,

On 2/9/2022 4:16 PM, Peter Zijlstra wrote:
> On Mon, Feb 07, 2022 at 09:29:21PM +0530, K Prateek Nayak wrote:
>> Neither the sched/tip nor Mel's v5 patchset [1] provides an optimal
>> new-task wakeup strategy when the tasks are affined to a subset of cpus
>> which can result in piling of tasks on the same set of CPU in a NUMA
>> group despite there being other cpus in a different NUMA group where the
>> task could have run in. 
> Where does this affinity come from?

The affinity comes from limiting the process to run on certain subset
of available cpus by modifying the cpus_ptr member of task_struck
of process via taskset or numactl.

---
Thanks and Regards
Prateek