From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
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: Thu, 21 May 2020 12:33:05 +0800 [thread overview]
Message-ID: <20200521043305.GA741019@T590> (raw)
In-Reply-To: <9249e1cc-b6f2-010e-78d2-ead5a1b93464@acm.org>
On Wed, May 20, 2020 at 08:50:56PM -0700, Bart Van Assche wrote:
> 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?
No.
If vector 3 is for covering hw queue 12 ~ 15, the vector shouldn't be
shutdown when cpu 14 is offline.
Also I am pretty sure that we don't do this way with managed IRQ. And
non-managed IRQ will be migrated to other online cpus during cpu offline,
so not an issue at all. See migrate_one_irq().
Thanks,
Ming
next prev parent reply other threads:[~2020-05-21 4:33 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
2020-05-21 4:33 ` Ming Lei [this message]
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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