linux-kernel - Re: [PATCH v6 3/9] nvme-pci: use block layer helpers to calculate num of queues

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Message-ID: <66cd13b0-3339-4495-8d1a-fae3211f92b9@flourine.local>
Date: Wed, 14 May 2025 18:12:04 +0200
From: Daniel Wagner <dwagner@...e.de>
To: Ming Lei <ming.lei@...hat.com>
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>, Frederic Weisbecker <frederic@...nel.org>, 
	Mel Gorman <mgorman@...e.de>, Hannes Reinecke <hare@...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 3/9] nvme-pci: use block layer helpers to calculate
 num of queues

On Fri, May 09, 2025 at 09:47:31AM +0800, Ming Lei wrote:
> On Thu, Apr 24, 2025 at 08:19:42PM +0200, Daniel Wagner wrote:
> > Multiqueue devices should only allocate queues for the housekeeping CPUs
> > when isolcpus=io_queue is set. This avoids that the isolated CPUs get
> > disturbed with OS workload.
> 
> The commit log needs to be updated:
> 
> - io_queue isn't introduced yet
> 
> - this patch can only reduce nr_hw_queues, and queue mapping isn't changed
> yet, so nothing to do with
> 
>  "This avoids that the isolated CPUs get disturbed with OS workload"

What about:

  The calculation of the upper limit for queues does not depend solely on
  the number of possible CPUs; for example, the isolcpus kernel
  command-line option must also be considered.

  To account for this, the block layer provides a helper function to
  retrieve the maximum number of queues. Use it to set an appropriate
  upper queue number limit.

I would use this version for the other patches as well,
s/possible/online/ where necessary.