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From: Bart Van Assche <bvanassche@acm.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
	Hannes Reinecke <hare@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: blk-mq: improvement CPU hotplug (simplified version) v3
Date: Wed, 20 May 2020 20:50:56 -0700	[thread overview]
Message-ID: <9249e1cc-b6f2-010e-78d2-ead5a1b93464@acm.org> (raw)
In-Reply-To: <20200521025744.GC735749@T590>

On 2020-05-20 19:57, Ming Lei wrote:
> On Wed, May 20, 2020 at 02:46:52PM -0700, Bart Van Assche wrote:
>> If the CPU to which one of these interrupt vectors has
>> been assigned is hotplugged, does that mean that four hardware queues
>> have to be quiesced instead of only one as is done in patch 6/6?
> 
> No, one hctx only becomes inactive after each CPU in hctx->cpumask is offline.
> No matter how interrupt vector is assigned to hctx, requests shouldn't
> be dispatched to that hctx any more.

Since I haven't found an answer to my question in your reply I will
rephrase my question. Suppose that there are 16 CPU cores, 16 hardware
queues and that hctx->cpumask of each hardware queue i only contains CPU
i. Suppose that four interrupt vectors (0, 1, 2 and 3) are used to
report the completions for these hardware queues. Suppose that interrupt
vector 3 is associated with hardware queues 12, 13, 14 and 15, and also
that interrupt vector 3 is mapped to CPU core 14. My interpretation of
patch 6/6 is that it will only quiesce hardware queue 14 but none of the
other hardware queues associated with the same interrupt vector
(hardware queues 12, 13 and 15). Isn't that a bug?

Thanks,

Bart.

  reply	other threads:[~2020-05-21  3:51 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-20 17:06 blk-mq: improvement CPU hotplug (simplified version) v3 Christoph Hellwig
2020-05-20 17:06 ` [PATCH 1/6] blk-mq: remove the bio argument to ->prepare_request Christoph Hellwig
2020-05-20 18:16   ` Bart Van Assche
2020-05-22  9:11   ` Hannes Reinecke
2020-05-20 17:06 ` [PATCH 2/6] blk-mq: simplify the blk_mq_get_request calling convention Christoph Hellwig
2020-05-20 18:22   ` Bart Van Assche
2020-05-22  9:13   ` Hannes Reinecke
2020-05-20 17:06 ` [PATCH 3/6] blk-mq: move more request initialization to blk_mq_rq_ctx_init Christoph Hellwig
2020-05-20 20:10   ` Bart Van Assche
2020-05-20 17:06 ` [PATCH 4/6] blk-mq: open code __blk_mq_alloc_request in blk_mq_alloc_request_hctx Christoph Hellwig
2020-05-22  9:17   ` Hannes Reinecke
2020-05-20 17:06 ` [PATCH 5/6] blk-mq: add blk_mq_all_tag_iter Christoph Hellwig
2020-05-20 20:24   ` Bart Van Assche
2020-05-27  6:05     ` Christoph Hellwig
2020-05-22  9:18   ` Hannes Reinecke
2020-05-20 17:06 ` [PATCH 6/6] blk-mq: drain I/O when all CPUs in a hctx are offline Christoph Hellwig
2020-05-22  9:25   ` Hannes Reinecke
2020-05-25  9:20     ` Ming Lei
2020-05-20 21:46 ` blk-mq: improvement CPU hotplug (simplified version) v3 Bart Van Assche
2020-05-21  2:57   ` Ming Lei
2020-05-21  3:50     ` Bart Van Assche [this message]
2020-05-21  4:33       ` Ming Lei
2020-05-21 19:15         ` Bart Van Assche
2020-05-22  2:39           ` Ming Lei
2020-05-22 14:47             ` Keith Busch
2020-05-23  3:05               ` Ming Lei
2020-05-23 15:19             ` Bart Van Assche
2020-05-25  4:09               ` Ming Lei
2020-05-25 15:32                 ` Bart Van Assche
2020-05-25 16:38                   ` Keith Busch
2020-05-26  0:37                   ` Ming Lei

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