linux-kernel - Re: [PATCH] blk-mq: make synchronous hw

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Message-ID: <20211213190529.j54qikq7mk5zuc3o@offworld>
Date:   Mon, 13 Dec 2021 11:05:29 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     axboe@...nel.dk, bigeasy@...utronix.de, tglx@...utronix.de,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH] blk-mq: make synchronous hw_queue runs RT friendly

On Mon, 13 Dec 2021, Christoph Hellwig wrote:
>But more importantly:  why isn't migrate_disable/enable doing the right
>thing for !PREEMPT_RT to avoid this mess?

Please see Peter's description of the situation in af449901b84.

While I'm not at all a fan of sprinkling migrate_disabling around code,
I didn't want to add any overhead for the common case. If this, however,
were not an issue (if most cases are async runs, for example) the ideal
solution I think would be to just pin current to the hctx->cpumask.

Thanks,
Davidlohr