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Date:   Wed, 27 Jan 2021 12:23:31 +0100
From:   Daniel Wagner <dwagner@suse.de>
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Christoph Hellwig <hch@infradead.org>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 3/3 v2] blk-mq: Use llist_head for blk_cpu_done
Message-ID: <20210127112331.bew6os5jfyvjzhwj@beryllium.lan>
References: <20210123201027.3262800-1-bigeasy@linutronix.de>
 <20210123201027.3262800-4-bigeasy@linutronix.de>
 <20210125083012.GD942655@infradead.org>
 <20210125083204.ahddujk5m6njwbju@linutronix.de>
 <20210125083903.GB945284@infradead.org>
 <20210125095412.qxknd2vbsmgtrhqb@linutronix.de>
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On Mon, Jan 25, 2021 at 10:54:12AM +0100, Sebastian Andrzej Siewior wrote:
> With llist_head it is possible to avoid the locking (the irq-off region)
> when items are added. This makes it possible to add items on a remote
> CPU without additional locking.
> llist_add() returns true if the list was previously empty. This can be
> used to invoke the SMP function call / raise sofirq only if the first
> item was added (otherwise it is already pending).
> This simplifies the code a little and reduces the IRQ-off regions.
> 
> blk_mq_raise_softirq() needs a preempt-disable section to ensure the
> request is enqueued on the same CPU as the softirq is raised.
> Some callers (USB-storage) invoke this path in preemptible context.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

I did a quick test run with the whole series. Looks good.

Reviewed-by: Daniel Wagner <dwagner@suse.de>