linux-kernel - Re: [RFC PATCH v1] blk-mq: isolate CPUs from hctx

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Message-ID: <67e8e089-4df2-4175-851a-4b49b964eca4@redhat.com>
Date: Fri, 15 Nov 2024 16:37:00 -0500
From: Waiman Long <llong@...hat.com>
To: Costa Shulyupin <costa.shul@...hat.com>, Michal Koutný
 <mkoutny@...e.com>
Cc: ming.lei@...hat.com, Jens Axboe <axboe@...nel.dk>,
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Daniel Wagner <dwagner@...e.de>
Subject: Re: [RFC PATCH v1] blk-mq: isolate CPUs from hctx


On 11/15/24 3:25 PM, Costa Shulyupin wrote:
> Hello Michal.
>
> Isolation of CPUs from blk_mq_hw_ctx during boot is already handled on
> call hierarchy:
> ...
>          nvme_probe()
>                  nvme_alloc_admin_tag_set()
>                          blk_mq_alloc_queue()
>                                  blk_mq_init_allocated_queue()
>                                          blk_mq_map_swqueue()
>
> blk_mq_map_swqueue() performs:
> for_each_cpu(cpu, hctx->cpumask) {
>          if (cpu_is_isolated(cpu))
>                  cpumask_clear_cpu(cpu, hctx->cpumask);
> }
>
> static inline bool cpu_is_isolated(int cpu)
> {
>          return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
>                  !housekeeping_test_cpu(cpu, HK_TYPE_TICK) ||
>                 cpuset_cpu_is_isolated(cpu);
> }

cpuset_cpu_is_isolated() can be removed once the cpumasks can be changed 
dynamically.

Cheers,
Longman