linux-kernel - Re: [PATCH v3 15/15] blk-mq: use hk cpus only when isolcpus=io

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Message-ID: <ba8a2ccd-1893-42e1-8ed9-dde6c43a2c95@flourine.local>
Date: Tue, 13 Aug 2024 14:53:46 +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>, "Martin K. Petersen" <martin.petersen@...cle.com>, 
	John Garry <john.g.garry@...cle.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
	Jason Wang <jasowang@...hat.com>, Kashyap Desai <kashyap.desai@...adcom.com>, 
	Sumit Saxena <sumit.saxena@...adcom.com>, Shivasharan S <shivasharan.srikanteshwara@...adcom.com>, 
	Chandrakanth patil <chandrakanth.patil@...adcom.com>, Sathya Prakash Veerichetty <sathya.prakash@...adcom.com>, 
	Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>, Nilesh Javali <njavali@...vell.com>, 
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Subject: Re: [PATCH v3 15/15] blk-mq: use hk cpus only when isolcpus=io_queue
 is enabled

On Fri, Aug 09, 2024 at 11:23:58PM GMT, Ming Lei wrote:
> From above implementation, "isolcpus=io_queue" is actually just one
> optimization on "isolcpus=managed_irq", and there isn't essential
> difference between the two.

Indeed, the two versions do not differ so much. I understood, that you
really want to keep managed_irq as it currently is and that's why I
thought we need io_queue.

> And I'd suggest to optimize 'isolcpus=managed_irq' directly, such as:
> 
> - reduce nr_queues or numgrps for group_cpus_evenly() according to
> house-keeping cpu mask

Okay.

> - spread house-keeping & isolate cpu mask evenly on each queue, and
> you can use the existed two-stage spread for doing that

Sure if we can get the spreading sorted out so that not all isolcpus are
mapped to the first hctx.

Thanks,
Daniel