Re: [RFC PATCH v2 1/1] scsi: mpi3mr: Introduce smp_affinity_enable module parameter

[John Garry <john.g.garry@oracle.com>]

On 19/06/2025 20:35, Aaron Tomlin wrote:
> 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.
> Hi John,
> 
> I'm trying to understand this better. If I'm not mistaken, modifying
> /sys/block/[device]/queue/rq_affinity impacts where requests are processed.
> Could you clarify how this would prevent an IRQ from being delivered to an
> isolated CPU?

If you echo 2 > /sys/block/[device]/queue/rq_affinity, then completions 
will occur on the same CPU which their originated. And through taskset, 
if you keep the processes generating traffic on a certain group of CPUs, 
then other CPUs should not see any loading from those same processes.

I am assuming that there is a one-to-one CPU <-> HW queue relationship.

That's my unverified idea...