linux-kernel - Re: [PATCH v5 8/9] blk-mq: issue warning when offlining hctx with online isolcpus

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Message-ID: <Z4HoN0F0cKD5G16F@fedora>
Date: Sat, 11 Jan 2025 11:40:39 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Daniel Wagner <wagi@...nel.org>
Cc: 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>,
	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 v5 8/9] blk-mq: issue warning when offlining hctx with
 online isolcpus

Hi Daniel,

On Fri, Jan 10, 2025 at 05:26:46PM +0100, Daniel Wagner wrote:
> When isolcpus=managed_irq is enabled, and the last housekeeping CPU for
> a given hardware context goes offline, there is no CPU left which
> handles the IOs anymore. If isolated CPUs mapped to this hardware
> context are online and an application running on these isolated CPUs
> issue an IO this will lead to stalls.
> 
> The kernel will not schedule IO to isolated CPUS thus this avoids IO
> stalls.
> 
> Thus issue a warning when housekeeping CPUs are offlined for a hardware
> context while there are still isolated CPUs online.

Why do you continue to send patch without addressing the fundamental regression?

This patchset does break existed applications which can't follow the new
rule of offlining CPU in order.

Again, it violates no-regression rule of kernel development.


Thanks,
Ming