linux-kernel - Re: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request

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Message-ID: <87tv0av1gu.fsf@nanos.tec.linutronix.de>
Date:   Wed, 20 May 2020 21:41:05 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Ming Lei <ming.lei@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        John Garry <john.garry@...wei.com>,
        Bart Van Assche <bvanassche@....org>,
        Hannes Reinecke <hare@...e.com>, io-uring@...r.kernel.org
Subject: Re: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx

Jens Axboe <axboe@...nel.dk> writes:
> On 5/20/20 8:45 AM, Jens Axboe wrote:
>> It just uses kthread_create_on_cpu(), nothing home grown. Pretty sure
>> they just break affinity if that CPU goes offline.
>
> Just checked, and it works fine for me. If I create an SQPOLL ring with
> SQ_AFF set and bound to CPU 3, if CPU 3 goes offline, then the kthread
> just appears unbound but runs just fine. When CPU 3 comes online again,
> the mask appears correct.

When exactly during the unplug operation is it unbound?

Thanks,

        tglx