linux-kernel - Re: [RFC][PATCH v2 08/10] smp,irq_work: Use the new irq

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Message-ID: <20200820061927.GA6447@lst.de>
Date:   Thu, 20 Aug 2020 08:19:27 +0200
From:   Christoph Hellwig <hch@....de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, will@...nel.org, paulmck@...nel.org,
        hch@....de, axboe@...nel.dk, chris@...is-wilson.co.uk,
        davem@...emloft.net, kuba@...nel.org, fweisbec@...il.com,
        oleg@...hat.com, vincent.guittot@...aro.org
Subject: Re: [RFC][PATCH v2 08/10] smp,irq_work: Use the new irq_work API

On Tue, Aug 18, 2020 at 12:51:10PM +0200, Peter Zijlstra wrote:
>  	if (blk_mq_complete_need_ipi(rq)) {
> -		INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
> -		smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd);
> +		rq->work = IRQ_WORK_INIT_HARD(__blk_mq_complete_request_remote);
> +		irq_work_queue_remote_static(rq->mq_ctx->cpu, &rq->work);

So given the caller synchronization / use once semantics does it even
make sense to split the init vs call part here?  What about:

		irq_work_queue_remote_static(&rq->work, rq->mq_ctx->cpu,
					    __blk_mq_complete_request_remote);

instead?  And btw, I'm not sure what the "static" stand for.  Maybe
irq_work_queue_remote_once?