Re: [PATCH v6 1/1] block/blk-mq: use atomic_t for quiesce_depth to avoid lock contention on RT

[Bart Van Assche]

On 5/6/26 9:47 AM, Sebastian Andrzej Siewior wrote:
> On 2026-05-06 09:14:33 [+0200], Bart Van Assche wrote:
> > If the atomic_inc() in blk_mq_quiesce_queue_nowait() is protected by
> > hctx->queue->queue_lock then the above code doesn't have to be modified.
>
> But wouldn't the atomic_inc + barrier avoid the need to have the lock?
> Isn't this a normal pattern? If the lock is kept, we could use
> non-atomic ops here then. But this avoids having the lock.

I strongly prefer a spinlock + non-atomic variables rather than using an
atomic variable and barriers because algorithms that use a spinlock are
easier to verify.

Thanks,

Bart.