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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: Sat, 23 May 2020 08:19:58 -0700
Message-ID: <26169cd9-49b8-b949-aaa3-9745e821c86c@acm.org> (raw)
In-Reply-To: <20200522023923.GC755458@T590>

On 2020-05-21 19:39, Ming Lei wrote:
> You may argue that two hw queue may share single managed interrupt, that
> is possible if driver plays the trick. But if driver plays the trick in
> this way, it is driver's responsibility to guarantee that the managed
> irq won't be shutdown if either of the two hctxs are active, such as,
> making sure that hctx->cpumask + hctx->cpumask <= this managed interrupt's affinity.
> It is definitely one strange enough case, and this patch doesn't
> suppose to cover this strange case. But, this patch won't break this
> case. Also just be curious, do you have such in-tree case? and are you
> sure the driver uses managed interrupt?

I'm concerned about the block drivers that use RDMA (NVMeOF, SRP, iSER,
...). The functions that accept an interrupt vector argument
(comp_vector), namely ib_alloc_cq() and ib_create_cq(), can be used in
such a way that completion interrupts are handled on another CPU than
those in hctx->cpumask.

Bart.

  parent reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-20 17:06 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
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 [this message]
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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