On 05/03/21 20:25, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Valentin Schneider [mailto:valentin.schneider@arm.com] Sent: Saturday, March 6, 2021 12:49 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; vincent.guittot@linaro.org; mingo@redhat.com; peterz@infradead.org; juri.lelli@redhat.com; dietmar.eggemann@arm.com; rostedt@goodmis.org; bsegall@google.com; mgorman@suse.de Cc: linux-kernel@vger.kernel.org; linuxarm@openeuler.org; Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Subject: Re: [PATCH] sched/topology: remove redundant cpumask_and in init_overlap_sched_group
On 05/03/21 11:29, Barry Song wrote:
mask is built in build_balance_mask() by for_each_cpu(i, sg_span), so it must be a subset of sched_group_span(sg).
So we should indeed have
cpumask_subset(sched_group_span(sg), mask)
but that doesn't imply
cpumask_first(sched_group_span(sg)) == cpumask_first(mask)
does it? I'm thinking if in your topology of N CPUs, CPUs 0 and N-1 are the furthest away, you will most likely hit
It is true: cpumask_first(sched_group_span(sg)) != cpumask_first(mask)
but
cpumask_first_and(sched_group_span(sg), mask) = cpumask_first(mask)
since mask is always subset of sched_group_span(sg).
You're right, I read it the wrong way around, sorry about that.
Reviewed-by: Valentin Schneider Valentin.Schneider@arm.com