linux-kernel - Re: [PATCH v2] sched_ext: Introduce LLC awareness to the default idle selection policy

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Message-ID: <Zxf4-DewpSO8Lcsg@slm.duckdns.org>
Date: Tue, 22 Oct 2024 09:11:52 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: Introduce LLC awareness to the default
 idle selection policy

Hello,

On Tue, Oct 22, 2024 at 04:55:51PM +0200, Andrea Righi wrote:
...
> Thinking more about this, we can avoid re-generating the llc_cpus
> cpumask when the task can run on all CPUs (likely the majority of the
> cases) and it's probably more efficient to check for
> cpumask_equal(p->cpus_ptr, cpu_possible_mask) and just use llc_mask in
> this case.

At the simplest, we can just skip llc-aware idle picking if not all CPUs are
allowed. Also, it's probably cheaper to test p->nr_cpus_allowed than testing
cpus_ptr.

> We could also optimize tasks that can only run on 1 CPU, but we never
> call ops.select_cpu() for them, they're just skipped in
> select_task_rq(), so I'm not sure if we should handle this special case
> (maybe I can add a comment, to make it more clear).

Yeah, a comment can be helpful.

Thanks.

-- 
tejun