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From: Ming Lei <ming.lei@redhat.com>
To: Keith Busch <kbusch@kernel.org>
Cc: Sagi Grimberg <sagi@grimberg.me>, Long Li <longli@microsoft.com>,
	linux-nvme@lists.infradead.org, Jens Axboe <axboe@fb.com>,
	Nadolski Edmund <edmund.nadolski@intel.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V3 2/2] nvme-pci: check CQ after batch submission for Microsoft device
Date: Thu, 14 Nov 2019 16:56:43 +0800	[thread overview]
Message-ID: <20191114085643.GA4213@ming.t460p> (raw)
In-Reply-To: <20191114045643.GA97802@C02WT3WMHTD6>

On Wed, Nov 13, 2019 at 09:56:43PM -0700, Keith Busch wrote:
> On Thu, Nov 14, 2019 at 10:59:17AM +0800, Ming Lei wrote:
> > @@ -912,6 +917,10 @@ static blk_status_t nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
> >  
> >  	blk_mq_start_request(req);
> >  	nvme_submit_cmd(nvmeq, &cmnd, bd->last);
> > +
> > +	if (bd->last && test_bit(NVMEQ_CHECK_CQ, &nvmeq->flags))
> > +		nvme_check_cq(nvmeq);
> > +
> 
> You've given this quirk a special completion handler, how about giving
> it a special queue_rq as well. Then you can check the completion queue
> during submission while holding the same lock as before.

We can do that, either we have to pass one extra 'check_cq' parameter to
common helper or duplicate a nvme_queue_rq_quick(). Not sure what benefit
we can get by this way, given test_bit(nvmeq->flags) is always close to
zero cost. 

Also if same lock is held in both submission & completion for the quirk,
the lock contention will be increased for the quirk since the lock has
to cover command submission, which shouldn't be needed.


Thanks,
Ming


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  reply	other threads:[~2019-11-14  8:57 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-14  2:59 [PATCH V3 0/2] nvme-pci: check CQ after batch submission for Microsoft device Ming Lei
2019-11-14  2:59 ` [PATCH V3 1/2] nvme-pci: move sq/cq_poll lock initialization into nvme_init_queue Ming Lei
2019-11-14  2:59 ` [PATCH V3 2/2] nvme-pci: check CQ after batch submission for Microsoft device Ming Lei
2019-11-14  4:56   ` Keith Busch
2019-11-14  8:56     ` Ming Lei [this message]
2019-11-21  3:11 ` [PATCH V3 0/2] " Ming Lei
2019-11-21  6:14   ` Christoph Hellwig
2019-11-21  7:46     ` Ming Lei
2019-11-21 15:45       ` Keith Busch
2019-11-22  9:44         ` Ming Lei
2019-11-22  9:57           ` Christoph Hellwig
2019-11-22 10:25             ` Ming Lei
2019-11-22 14:04               ` Jens Axboe
2019-11-22 21:49                 ` Ming Lei
2019-11-22 21:58                   ` Jens Axboe
2019-11-22 22:30                     ` Ming Lei

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