linux-kernel - Re: [RFC PATCH v2 1/1] scsi: mpi3mr: Introduce smp_affinity

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Message-ID: <aFjjf3qbuEOeWUjt@infradead.org>
Date: Sun, 22 Jun 2025 22:17:51 -0700
From: Christoph Hellwig <hch@...radead.org>
To: John Garry <john.g.garry@...cle.com>, Daniel Wagner <wagi@...nel.org>
Cc: "Sean A." <sean@...e.io>,
	"James.Bottomley@...senpartnership.com" <James.Bottomley@...senpartnership.com>,
	"atomlin@...mlin.com" <atomlin@...mlin.com>,
	"kashyap.desai@...adcom.com" <kashyap.desai@...adcom.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"martin.petersen@...cle.com" <martin.petersen@...cle.com>,
	"mpi3mr-linuxdrv.pdl@...adcom.com" <mpi3mr-linuxdrv.pdl@...adcom.com>,
	"sreekanth.reddy@...adcom.com" <sreekanth.reddy@...adcom.com>,
	"sumit.saxena@...adcom.com" <sumit.saxena@...adcom.com>
Subject: Re: [RFC PATCH v2 1/1] scsi: mpi3mr: Introduce smp_affinity_enable
 module parameter

On Wed, Jun 18, 2025 at 07:49:16AM +0100, John Garry wrote:
> BTW, if you use taskset to set the affinity of a process and ensure that
> /sys/block/xxx/queue/rq_affinity is set so that we complete on same CPU as
> submitted, then I thought that this would ensure that interrupts are not
> bothering other CPUs.

The RT folks want to not even have interrupts on the application CPUs.
That's perfectly reasonable and a common request.  Why doing driver
hacks as in this patch and many others is so completely insane.  Instead
we need common functionality for that.  The core irq layer has added
them for managed interrupts, and Daniel has been working on the blk-mq side
for a while.