linux-kernel - Re: [PATCH v6 6/9] isolation: introduce io

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Message-ID: <706b08be-781c-45d6-8c16-93d6d97b4330@flourine.local>
Date: Wed, 14 May 2025 18:08:40 +0200
From: Daniel Wagner <dwagner@...e.de>
To: Ming Lei <ming.lei@...hat.com>
Cc: Hannes Reinecke <hare@...e.de>, 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>, 
	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 v6 6/9] isolation: introduce io_queue isolcpus type

On Fri, May 09, 2025 at 10:04:18AM +0800, Ming Lei wrote:
> > 			io_queue
> > 			  Isolate from IO queue work caused by multiqueue
> > 			  device drivers. Restrict the placement of
> > 			  queues to housekeeping CPUs only, ensuring that
> > 			  all IO work is processed by a housekeeping CPU.
> > 
> > 			  Note: When an isolated CPU issues an IO, it is
> > 			  forwarded to a housekeeping CPU. This will
> > 			  trigger a software interrupt on the completion
> > 			  path.
> > 
> > 			  Note: It is not possible to offline housekeeping
> > 			  CPUs that serve isolated CPUs.
> 
> This patch adds kernel parameter only, but not apply it at all, the above
> words just confuses everyone, so I'd suggest to not expose the kernel
> command line & document until the whole mechanism is supported.

I'll add this doc update as last patch.

> Especially 'irqaffinity=0 isolcpus=io_queue' requires the application
> to offline CPU in order, which has to be documented:
> 
> https://lore.kernel.org/all/cc5e44dd-e1dc-4f24-88d9-ce45a8b0794f@flourine.local/

Okay, so you want me to extend the above second note in this case. I'll
give it a go.