linux-kernel - Re: [PATCH v7 09/10] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

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Message-ID: <w5rxrdtvk7n473stsjqhq4dvtdqearnsuu7yw63e6lhc5tzszg@dnrl22hyr7br>
Date: Mon, 7 Jul 2025 21:31:40 -0400
From: Aaron Tomlin <atomlin@...mlin.com>
To: Daniel Wagner <wagi@...nel.org>, Ming Lei <ming.lei@...hat.com>
Cc: Daniel Wagner <wagi@...nel.org>, Jens Axboe <axboe@...nel.dk>, 
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, 
	"Michael S. Tsirkin" <mst@...hat.com>, "Martin K. Petersen" <martin.petersen@...cle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Costa Shulyupin <costa.shul@...hat.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Valentin Schneider <vschneid@...hat.com>, 
	Waiman Long <llong@...hat.com>, Frederic Weisbecker <frederic@...nel.org>, 
	Mel Gorman <mgorman@...e.de>, Hannes Reinecke <hare@...e.de>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, 
	linux-nvme@...ts.infradead.org, megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org, 
	storagedev@...rochip.com, virtualization@...ts.linux.dev, 
	GR-QLogic-Storage-Upstream@...vell.com
Subject: Re: [PATCH v7 09/10] blk-mq: prevent offlining hk CPUs with
 associated online isolated CPUs

On Mon, Jul 07, 2025 at 03:44:30PM +0800, Ming Lei wrote:
> On Wed, Jul 02, 2025 at 06:33:59PM +0200, Daniel Wagner wrote:
> > When isolcpus=io_queue is enabled, and the last housekeeping CPU for a
> > given hctx goes offline, there would be no CPU left to handle I/O. To
> > prevent I/O stalls, prevent offlining housekeeping CPUs that are still
> > serving isolated CPUs.
> > 
> > When isolcpus=io_queue is enabled and the last housekeeping CPU
> > for a given hctx goes offline, no CPU would be left to handle I/O.
> > To prevent I/O stalls, disallow offlining housekeeping CPUs that are
> > still serving isolated CPUs.
> 
> If you do so, cpu offline is failed, and this change is user visible, please
> document the cpu offline failure limit on Documentation/admin-guide/kernel-parameters.txt.
> in the next patch.
> 
> Thanks,
> Ming

+1

-- 
Aaron Tomlin