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

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Message-ID: <dd4719dc-5ac4-44d9-bccb-e867d322864e@flourine.local>
Date: Fri, 25 Apr 2025 09:32:16 +0200
From: Daniel Wagner <dwagner@...e.de>
To: Hannes Reinecke <hare@...e.de>
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>, Ming Lei <ming.lei@...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, Apr 25, 2025 at 08:26:22AM +0200, Hannes Reinecke wrote:
> On 4/24/25 20:19, Daniel Wagner wrote:
> > Multiqueue drivers spreading IO queues on all CPUs for optimal
> > performance. The drivers are not aware of the CPU isolated requirement
> > and will spread all queues ignoring the isolcpus configuration.
> > 
> > Introduce a new isolcpus mask which allows the user to define on which
> > CPUs IO queues should be placed. This is similar to the managed_irq but
> > for drivers which do not use the managed IRQ infrastructure.
> > 
> > Signed-off-by: Daniel Wagner <wagi@...nel.org>
> > ---
> >   include/linux/sched/isolation.h | 1 +
> >   kernel/sched/isolation.c        | 7 +++++++
> >   2 files changed, 8 insertions(+)
> > 
> Reviewed-by: Hannes Reinecke <hare@...e.de>

Just realized I forgot to also add some document on this new argument:

			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.