From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
Bart Van Assche <bvanassche@acm.org>,
Hannes Reinecke <hare@suse.com>,
io-uring@vger.kernel.org
Subject: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx
Date: Wed, 20 May 2020 10:03:57 +0200 [thread overview]
Message-ID: <20200520080357.GA4197@lst.de> (raw)
In-Reply-To: <20200520030424.GI416136@T590>
On Wed, May 20, 2020 at 11:04:24AM +0800, Ming Lei wrote:
> On Wed, May 20, 2020 at 09:18:23AM +0800, Ming Lei wrote:
> > On Tue, May 19, 2020 at 05:30:00PM +0200, Christoph Hellwig wrote:
> > > On Tue, May 19, 2020 at 09:54:20AM +0800, Ming Lei wrote:
> > > > As Thomas clarified, workqueue hasn't such issue any more, and only other
> > > > per CPU kthreads can run until the CPU clears the online bit.
> > > >
> > > > So the question is if IO can be submitted from such kernel context?
> > >
> > > What other per-CPU kthreads even exist?
> >
> > I don't know, so expose to wider audiences.
>
> One user is io uring with IORING_SETUP_SQPOLL & IORING_SETUP_SQ_AFF, see
> io_sq_offload_start(), and it is a IO submission kthread.
As far as I can tell that code is buggy, as it still needs to migrate
the thread away when the cpu is offlined. This isn't a per-cpu kthread
in the sene of having one for each CPU.
Jens?
next parent reply other threads:[~2020-05-20 8:04 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200518093155.GB35380@T590>
[not found] ` <87imgty15d.fsf@nanos.tec.linutronix.de>
[not found] ` <20200518115454.GA46364@T590>
[not found] ` <20200518131634.GA645@lst.de>
[not found] ` <20200518141107.GA50374@T590>
[not found] ` <20200518165619.GA17465@lst.de>
[not found] ` <20200519015420.GA70957@T590>
[not found] ` <20200519153000.GB22286@lst.de>
[not found] ` <20200520011823.GA415158@T590>
[not found] ` <20200520030424.GI416136@T590>
2020-05-20 8:03 ` Christoph Hellwig [this message]
2020-05-20 14:45 ` io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx 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
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