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

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Date: Sat, 11 May 2024 07:50:21 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Keith Busch <kbusch@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...a.com>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [PATCH 2/2] nvme-pci: allow unmanaged interrupts

On Fri, May 10, 2024 at 10:20:02AM -0600, Keith Busch wrote:
> 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.

Can you explain a bit why it is a no-op? If only isolated CPUs are
spread on one queue, there will be no IO originated from these isolated
CPUs, that is exactly what the isolation needs.



Thanks,
Ming