linux-kernel - Re: [PATCH 2/2] nvme-pci: allow unmanaged interrupts

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Message-ID: <Zj5JMqWRY187PqnD@kbusch-mbp.dhcp.thefacebook.com>
Date: Fri, 10 May 2024 10:20:02 -0600
From: Keith Busch <kbusch@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Keith Busch <kbusch@...a.com>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	ming.lei@...hat.com
Subject: Re: [PATCH 2/2] nvme-pci: allow unmanaged interrupts

On Fri, May 10, 2024 at 05:10:47PM +0200, Christoph Hellwig wrote:
> On Fri, May 10, 2024 at 07:14:59AM -0700, Keith Busch wrote:
> > From: Keith Busch <kbusch@...nel.org>
> > 
> > Some people _really_ want to control their interrupt affinity.
> 
> So let them argue why.  I'd rather have a really, really, really
> good argument for this crap, and I'd like to hear it from the horses
> mouth.

It's just prioritizing predictable user task scheduling for a subset of
CPUs instead of having consistently better storage performance.

We already have "isolcpus=managed_irq," parameter to prevent managed
interrupts from running on a subset of CPUs, so the use case is already
kind of supported. The problem with that parameter is it is a no-op if
the starting affinity spread contains only isolated CPUs.