From: Christoph Hellwig <hch@lst.de>
To: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Christoph Hellwig <hch@lst.de>,
axboe@kernel.dk, ming.lei@redhat.com, tj@kernel.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Chengming Zhou <zhouchengming@bytedance.com>
Subject: Re: [PATCH v2 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd
Date: Thu, 6 Jul 2023 16:39:46 +0200 [thread overview]
Message-ID: <20230706143946.GA15131@lst.de> (raw)
In-Reply-To: <f6f52b55-a991-1179-75cb-bf8fce8f6783@linux.dev>
On Thu, Jul 06, 2023 at 10:23:49PM +0800, Chengming Zhou wrote:
> Yes, should I change like below? Looks like much long code. :-)
>
> if (llist_add(&rq->ipi_list, &per_cpu(blk_cpu_done, cpu)))
> smp_call_function_single_async(cpu, &per_cpu(blk_cpu_csd, cpu));
Doesn't look bad too me.
>
>
> >
> > But I think this code has a rpboem when it is preemptd between
> > the llist_add and smp_call_function_single_async. We either need a
> > get_cpu/put_cpu around them, or instroduce a structure with the list
> > and csd, and then you can use one pointer from per_cpu and still ensure
> > the list and csd are for the same CPU.
> >
>
> cpu = rq->mq_ctx->cpu; So it's certainly the same CPU, right?
You're right of couse - cpu is the submitting cpu and not the current
one and thus not affected by preemption. Sorry for the noise.
next prev parent reply other threads:[~2023-07-06 14:39 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-29 11:03 [PATCH v2 0/4] blk-mq: optimize the size of struct request chengming.zhou
2023-06-29 11:03 ` [PATCH v2 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd chengming.zhou
2023-07-05 15:01 ` Ming Lei
2023-07-06 13:07 ` Christoph Hellwig
2023-07-06 14:23 ` Chengming Zhou
2023-07-06 14:39 ` Christoph Hellwig [this message]
2023-06-29 11:03 ` [PATCH v2 2/4] blk-flush: count inflight flush_data requests chengming.zhou
2023-07-05 15:10 ` Ming Lei
2023-07-06 13:08 ` Christoph Hellwig
2023-06-29 11:03 ` [PATCH v2 3/4] blk-flush: reuse rq queuelist in flush state machine chengming.zhou
2023-07-06 13:08 ` Christoph Hellwig
2023-06-29 11:03 ` [PATCH v2 4/4] blk-mq: delete unused completion_data in struct request chengming.zhou
2023-07-06 13:08 ` Christoph Hellwig
2023-07-06 14:31 ` Chengming Zhou
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