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

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Date:   Mon, 13 Dec 2021 05:07:04 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Davidlohr Bueso <dave@...olabs.net>
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

> +#ifndef CONFIG_PREEMPT_RT

Please don't add these silly inverted ifdefs.

> +static inline void blk_mq_start_sync_run_hw_queue(void)
> +{
> +	preempt_disable();
> +}
> +static inline void blk_mq_end_sync_run_hw_queue(void)
> +{
> +	preempt_enable();
> +}
> +#else
> +static inline void blk_mq_start_sync_run_hw_queue(void)
> +{
> +	migrate_disable();
> +}
> +static inline void blk_mq_end_sync_run_hw_queue(void)
> +{
> +	migrate_enable();
> +}
> +#endif

But more importantly:  why isn't migrate_disable/enable doing the right
thing for !PREEMPT_RT to avoid this mess?