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From: Sagi Grimberg <sagi@grimberg.me>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org
Cc: linux-nvme@lists.infradead.org, Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCH 5/5] blk-mq: support nested blk_mq_quiesce_queue()
Date: Wed, 29 Sep 2021 14:53:27 +0300	[thread overview]
Message-ID: <54b636d5-ede6-a700-4d02-4712db679234@grimberg.me> (raw)
In-Reply-To: <20210929041559.701102-6-ming.lei@redhat.com>



On 9/29/21 7:15 AM, Ming Lei wrote:
> Turns out that blk_mq_freeze_queue() isn't stronger[1] than
> blk_mq_quiesce_queue() because dispatch may still be in-progress after
> queue is frozen, and in several cases, such as switching io scheduler,
> updating nr_requests & wbt latency, we still need to quiesce queue as a
> supplement of freezing queue.
> 
> As we need to extend uses of blk_mq_quiesce_queue(), it is inevitable
> for us to need support nested quiesce, especailly we can't let
> unquiesce happen when there is quiesce originated from other contexts.

The serialization need is clear, but why is the nesting required?
In other words what is the harm is running the hw queue every time
we unquiesce?

WARNING: multiple messages have this Message-ID (diff)
From: Sagi Grimberg <sagi@grimberg.me>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org
Cc: linux-nvme@lists.infradead.org, Keith Busch <kbusch@kernel.org>
Subject: Re: [PATCH 5/5] blk-mq: support nested blk_mq_quiesce_queue()
Date: Wed, 29 Sep 2021 14:53:27 +0300	[thread overview]
Message-ID: <54b636d5-ede6-a700-4d02-4712db679234@grimberg.me> (raw)
In-Reply-To: <20210929041559.701102-6-ming.lei@redhat.com>



On 9/29/21 7:15 AM, Ming Lei wrote:
> Turns out that blk_mq_freeze_queue() isn't stronger[1] than
> blk_mq_quiesce_queue() because dispatch may still be in-progress after
> queue is frozen, and in several cases, such as switching io scheduler,
> updating nr_requests & wbt latency, we still need to quiesce queue as a
> supplement of freezing queue.
> 
> As we need to extend uses of blk_mq_quiesce_queue(), it is inevitable
> for us to need support nested quiesce, especailly we can't let
> unquiesce happen when there is quiesce originated from other contexts.

The serialization need is clear, but why is the nesting required?
In other words what is the harm is running the hw queue every time
we unquiesce?

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Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme

  reply	other threads:[~2021-09-29 11:53 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29  4:15 [PATCH 0/5] blk-mq: support nested queue quiescing Ming Lei
2021-09-29  4:15 ` Ming Lei
2021-09-29  4:15 ` [PATCH 1/5] nvme: add APIs for stopping/starting admin queue Ming Lei
2021-09-29  4:15   ` Ming Lei
2021-09-29  4:15 ` [PATCH 2/5] nvme: apply nvme API to quiesce/unquiesce " Ming Lei
2021-09-29  4:15   ` Ming Lei
2021-09-29  4:15 ` [PATCH 3/5] nvme: prepare for pairing quiescing and unquiescing Ming Lei
2021-09-29  4:15   ` Ming Lei
2021-09-29  4:15 ` [PATCH 4/5] nvme: paring quiesce/unquiesce Ming Lei
2021-09-29  4:15   ` Ming Lei
2021-09-29 11:49   ` Sagi Grimberg
2021-09-29 11:49     ` Sagi Grimberg
2021-09-29 15:28     ` Ming Lei
2021-09-29 15:28       ` Ming Lei
2021-09-29  4:15 ` [PATCH 5/5] blk-mq: support nested blk_mq_quiesce_queue() Ming Lei
2021-09-29  4:15   ` Ming Lei
2021-09-29 11:53   ` Sagi Grimberg [this message]
2021-09-29 11:53     ` Sagi Grimberg
2021-09-29 15:44     ` Ming Lei
2021-09-29 15:44       ` Ming Lei

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