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From: Thomas Gleixner <tglx@linutronix.de>
To: Christoph Hellwig <hch@lst.de>, Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx
Date: Mon, 18 May 2020 20:38:04 +0200
Message-ID: <87o8qlw0kz.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200518165619.GA17465@lst.de>

Christoph Hellwig <hch@lst.de> writes:

> On Mon, May 18, 2020 at 10:11:07PM +0800, Ming Lei wrote:
>> On Mon, May 18, 2020 at 03:16:34PM +0200, Christoph Hellwig wrote:
>> > On Mon, May 18, 2020 at 07:54:54PM +0800, Ming Lei wrote:
>> > > 
>> > > I guess I misunderstood your point, sorry for that.
>> > > 
>> > > The requirement is just that the request needs to be allocated on one online
>> > > CPU after INACTIVE is set, and we can use a workqueue to do that.
>> > 
>> > I've looked over the code again, and I'm really not sure why we need that.
>> > Presumable the CPU hotplug code ensures tasks don't get schedule on the
>> > CPU running the shutdown state machine, so if we just do a retry of the
>> 
>> percpu kthread still can be scheduled on the cpu to be online, see
>> is_cpu_allowed(). And bound wq has been used widely in fs code.
>
> s/to be online/to be offlined/ I guess.
>
> Shouldn't all the per-cpu kthreads also stop as part of the offlining?
> If they don't quiesce before the new blk-mq stop state I think we need
> to make sure they do.  It is rather pointless to quiesce the requests
> if a thread that can submit I/O is still live.

Which kthreads are you talking about?

Workqueues? CPU bound workqueues are shut down in
CPUHP_AP_WORKQUEUE_ONLINE state.

Thanks,

        tglx

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-18  6:39 blk-mq: improvement CPU hotplug (simplified version) v2 Christoph Hellwig
2020-05-18  6:39 ` [PATCH 1/9] blk-mq: split out a __blk_mq_get_driver_tag helper Christoph Hellwig
2020-05-18  6:39 ` [PATCH 2/9] blk-mq: remove the bio argument to ->prepare_request Christoph Hellwig
2020-05-18  6:39 ` [PATCH 3/9] blk-mq: simplify the blk_mq_get_request calling convention Christoph Hellwig
2020-05-18  6:39 ` [PATCH 4/9] blk-mq: merge blk_mq_rq_ctx_init into __blk_mq_alloc_request Christoph Hellwig
2020-05-18  6:39 ` [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx Christoph Hellwig
2020-05-18  8:32   ` Thomas Gleixner
2020-05-18  9:31     ` Ming Lei
2020-05-18 10:42       ` Thomas Gleixner
2020-05-18 11:54         ` Ming Lei
2020-05-18 13:16           ` Christoph Hellwig
2020-05-18 14:11             ` Ming Lei
2020-05-18 16:56               ` Christoph Hellwig
2020-05-18 18:38                 ` Thomas Gleixner [this message]
2020-05-18 18:45                   ` Christoph Hellwig
2020-05-18 18:59                     ` Thomas Gleixner
2020-05-19  1:54                 ` Ming Lei
2020-05-19 15:30                   ` Christoph Hellwig
2020-05-20  1:18                     ` Ming Lei
2020-05-20  3:04                       ` Ming Lei
2020-05-20  8:03                         ` io_uring vs CPU hotplug, was " Christoph Hellwig
2020-05-20 14:45                           ` Jens Axboe
2020-05-20 15:20                             ` Jens Axboe
2020-05-20 15:31                               ` Christoph Hellwig
2020-05-20 19:41                               ` Thomas Gleixner
2020-05-20 20:18                                 ` Jens Axboe
2020-05-20 22:14                                   ` Thomas Gleixner
2020-05-20 22:40                                     ` Jens Axboe
2020-05-21  2:27                                     ` Ming Lei
2020-05-21  8:13                                       ` Thomas Gleixner
2020-05-21  9:23                                         ` Ming Lei
2020-05-21 18:39                                           ` Thomas Gleixner
2020-05-21 18:45                                             ` Jens Axboe
2020-05-21 20:00                                               ` Thomas Gleixner
2020-05-22  1:57                                             ` Ming Lei
2020-05-18 18:47             ` Thomas Gleixner
2020-05-18 13:18           ` Thomas Gleixner
2020-05-18  6:39 ` [PATCH 6/9] blk-mq: don't set data->ctx and data->hctx in __blk_mq_alloc_request Christoph Hellwig
2020-05-18  6:39 ` [PATCH 7/9] blk-mq: disable preemption during allocating request tag Christoph Hellwig
2020-05-18  6:39 ` [PATCH 8/9] blk-mq: add blk_mq_all_tag_iter Christoph Hellwig
2020-05-18  6:39 ` [PATCH 9/9] blk-mq: drain I/O when all CPUs in a hctx are offline Christoph Hellwig
2020-05-18  8:42   ` John Garry
2020-05-18  9:21     ` Ming Lei
2020-05-18 11:49 ` blk-mq: improvement CPU hotplug (simplified version) v2 John Garry
2020-05-19 15:30   ` Christoph Hellwig
2020-05-19 17:17     ` John Garry
2020-05-20 14:35     ` John Garry

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