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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH V11 07/12] blk-mq: stop to handle IO and drain IO before hctx becomes inactive
Date: Thu, 14 May 2020 11:10:33 +0800	[thread overview]
Message-ID: <20200514031033.GJ2073570@T590> (raw)
In-Reply-To: <20200513115932.GC6297@lst.de>

On Wed, May 13, 2020 at 01:59:32PM +0200, Christoph Hellwig wrote:
> > +	if (unlikely(direct_issue && rq->mq_ctx->cpu != raw_smp_processor_id()))
> > +		smp_mb();
> > +	else
> > +		barrier();
> 
> Independ of the fact that I still think this is horrible and hacky,
> I also still don't see what the barrier() is trying to help with.

It is correct and clean to only add smp_mb() for ordering setting
rq->tag/assigning req and checking INACTIVE, and just a normal usage
of memory barrier.

barrier() is used in most likely case because smp_mb() is only required
when direct io issue process is migrated to other CPU, that seldom
happens, so just an optimization.

So I do not agree it is horrible and hacky.

Thanks,
Ming


  parent reply	other threads:[~2020-05-14  3:10 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13  3:47 [PATCH V11 00/12] blk-mq: improvement CPU hotplug Ming Lei
2020-05-13  3:47 ` [PATCH V11 01/12] block: clone nr_integrity_segments and write_hint in blk_rq_prep_clone Ming Lei
2020-05-13  3:47 ` [PATCH V11 02/12] block: add helper for copying request Ming Lei
2020-05-13  3:47 ` [PATCH V11 03/12] blk-mq: mark blk_mq_get_driver_tag as static Ming Lei
2020-05-13  3:47 ` [PATCH V11 04/12] blk-mq: assign rq->tag in blk_mq_get_driver_tag Ming Lei
2020-05-13  3:47 ` [PATCH V11 05/12] blk-mq: add blk_mq_all_tag_iter Ming Lei
2020-05-13 11:56   ` Christoph Hellwig
2020-05-13  3:47 ` [PATCH V11 06/12] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2020-05-13  6:35   ` Hannes Reinecke
2020-05-13 11:58   ` Christoph Hellwig
2020-05-14  0:33     ` Ming Lei
2020-05-13  3:47 ` [PATCH V11 07/12] blk-mq: stop to handle IO and drain IO before hctx becomes inactive Ming Lei
2020-05-13 11:59   ` Christoph Hellwig
2020-05-14  0:36     ` Ming Lei
2020-05-14  1:12     ` Bart Van Assche
2020-05-14  3:10     ` Ming Lei [this message]
2020-05-13  3:47 ` [PATCH V11 08/12] block: add blk_end_flush_machinery Ming Lei
2020-05-13 12:00   ` Christoph Hellwig
2020-05-13  3:48 ` [PATCH V11 09/12] blk-mq: add blk_mq_hctx_handle_dead_cpu for handling cpu dead Ming Lei
2020-05-13 12:06   ` Christoph Hellwig
2020-05-13  3:48 ` [PATCH V11 10/12] block: add request allocation flag of BLK_MQ_REQ_FORCE Ming Lei
2020-05-13 10:34   ` [PATCH V12 " Ming Lei
2020-05-13  3:48 ` [PATCH V11 11/12] blk-mq: re-submit IO in case that hctx is inactive Ming Lei
2020-05-13  9:21   ` John Garry
2020-05-13 12:21   ` Christoph Hellwig
2020-05-13 15:03     ` Bart Van Assche
2020-05-14  0:45       ` Ming Lei
2020-05-14  0:40     ` Ming Lei
2020-05-13  3:48 ` [PATCH V11 12/12] block: deactivate hctx when the hctx is actually inactive Ming Lei
2020-05-13  7:34 ` [PATCH V11 00/12] blk-mq: improvement CPU hotplug John Garry
2020-05-13 10:37   ` Ming Lei
2020-05-13 11:33     ` John Garry

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