linux-kernel - Re: [PATCH v2 3/3] lib/group_cpus.c: honor housekeeping config when grouping CPUs

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Message-ID: <b2ncik6c7xicsnzihhwfjjqood2yys52tzotohjnxj6o2mapg5@m364yzsjbvs2>
Date: Mon, 1 Jul 2024 09:08:32 +0200
From: Daniel Wagner <dwagner@...e.de>
To: Ming Lei <ming.lei@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>, 
	Sagi Grimberg <sagi@...mberg.me>, Thomas Gleixner <tglx@...utronix.de>, 
	Christoph Hellwig <hch@....de>, Frederic Weisbecker <fweisbecker@...e.com>, 
	Mel Gorman <mgorman@...e.de>, Hannes Reinecke <hare@...e.de>, 
	Sridhar Balaraman <sbalaraman@...allelwireless.com>, "brookxu.cn" <brookxu.cn@...il.com>, 
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v2 3/3] lib/group_cpus.c: honor housekeeping config when
 grouping CPUs

On Sun, Jun 30, 2024 at 09:39:59PM GMT, Ming Lei wrote:
> > Make group_cpus_evenly aware of isolcpus configuration and use the
> > housekeeping CPU mask as base for distributing the available CPUs into
> > groups.
> > 
> > Fixes: 11ea68f553e2 ("genirq, sched/isolation: Isolate from handling managed interrupts")
> 
> isolated CPUs are actually handled when figuring out irq effective mask,
> so not sure how commit 11ea68f553e2 is wrong, and what is fixed in this
> patch from user viewpoint?

IO queues are allocated/spread on the isolated CPUs and if there is an
thread submitting IOs from an isolated CPU it will cause noise on the
isolated CPUs. The question is this a use case you need/want to support?
We have customers who are complaining that even with isolcpus provided
they still see IO noise on the isolated CPUs.