linux-kernel - Re: [PATCH v7 05/10] scsi: Use block layer helpers to constrain queue affinity

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Message-ID: <d95de280-8cd7-4697-933a-37dc53f4c552@suse.de>
Date: Thu, 3 Jul 2025 08:43:01 +0200
From: Hannes Reinecke <hare@...e.de>
To: 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>
Cc: Aaron Tomlin <atomlin@...mlin.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 v7 05/10] scsi: Use block layer helpers to constrain queue
 affinity

On 7/2/25 18:33, Daniel Wagner wrote:
> Ensure that IRQ affinity setup also respects the queue-to-CPU mapping
> constraints provided by the block layer. This allows the SCSI drivers
> to avoid assigning interrupts to CPUs that the block layer has excluded
> (e.g., isolated CPUs).
> 
> Signed-off-by: Daniel Wagner <wagi@...nel.org>
> ---
>   drivers/scsi/fnic/fnic_isr.c              | 7 +++++--
>   drivers/scsi/hisi_sas/hisi_sas_v3_hw.c    | 1 +
>   drivers/scsi/megaraid/megaraid_sas_base.c | 5 ++++-
>   drivers/scsi/mpi3mr/mpi3mr_fw.c           | 6 +++++-
>   drivers/scsi/mpt3sas/mpt3sas_base.c       | 5 ++++-
>   drivers/scsi/pm8001/pm8001_init.c         | 1 +
>   drivers/scsi/qla2xxx/qla_isr.c            | 1 +
>   drivers/scsi/smartpqi/smartpqi_init.c     | 7 +++++--
>   8 files changed, 26 insertions(+), 7 deletions(-)
 >

All of these drivers are not aware of CPU hotplug, and as such
will not be notified when the number of CPUs changes.
But you use 'blk_mq_online_queue_affinity()' for all of these
drivers.
Wouldn't 'blk_mq_possible_queue_affinit()' a better choice here
to insulate against CPU hotplug effects?

Also some drivers which are using irq affinity (eg aacraid, lpfc) are
missing from these conversions. Why?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich