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

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Date: Mon, 1 Jul 2024 16:47:48 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Daniel Wagner <dwagner@...e.de>
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 Mon, Jul 01, 2024 at 10:19:25AM +0200, Daniel Wagner wrote:
> On Mon, Jul 01, 2024 at 03:21:13PM GMT, Ming Lei wrote:
> > On Mon, Jul 01, 2024 at 09:08:32AM +0200, Daniel Wagner wrote:
> > > 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?
> > 
> > I have talked RH Openshift team weeks ago and they have such usage.
> > 
> > userspace is free to run any application from isolated CPUs via 'taskset
> > -c' even though 'isolcpus=' is passed from command line.
> >
> > Kernel can not add such new constraint on userspace.
> 
> Okay, that is why I asked if we need an additional HK type.
> 
> > > We have customers who are complaining that even with isolcpus provided
> > > they still see IO noise on the isolated CPUs.
> > 
> > That is another issue, which has been fixed by the following patch:
> > 
> > a46c27026da1 blk-mq: don't schedule block kworker on isolated CPUs
> 
> I've checked our downstream kernels and we don't have this one yet. I'll
> ask our customer to test if this patch addressed their issue.

BTW, you need the following one too:

7b815817aa58 blk-mq: add helper for checking if one CPU is mapped to specified hctx

Thanks,
Ming