linux-kernel - Re: [PATCH V3 1/5] genirq/affinity: don't mark 'affd' as const

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Message-ID: <20190213213149.GB8027@localhost.localdomain>
Date:   Wed, 13 Feb 2019 14:31:49 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Sagi Grimberg <sagi@...mberg.me>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V3 1/5] genirq/affinity: don't mark 'affd' as const

On Wed, Feb 13, 2019 at 09:56:36PM +0100, Thomas Gleixner wrote:
> On Wed, 13 Feb 2019, Bjorn Helgaas wrote:
> > On Wed, Feb 13, 2019 at 06:50:37PM +0800, Ming Lei wrote:
> > > We have to ask driver to re-caculate set vectors after the whole IRQ
> > > vectors are allocated later, and the result needs to be stored in 'affd'.
> > > Also both the two interfaces are core APIs, which should be trusted.
> > 
> > s/re-caculate/recalculate/
> > s/stored in 'affd'/stored in '*affd'/
> > s/both the two/both/
> > 
> > This is a little confusing because you're talking about both "IRQ
> > vectors" and these other "set vectors", which I think are different
> > things.  I assume the "set vectors" are cpumasks showing the affinity
> > of the IRQ vectors with some CPUs?
> 
> I think we should drop the whole vector wording completely.
> 
> The driver does not care about vectors, it only cares about a block of
> interrupt numbers. These numbers are kernel managed and the interrupts just
> happen to have a CPU vector assigned at some point. Depending on the CPU
> architecture the underlying mechanism might not even be named vector.

Perhaps longer term we could move affinity mask creation from the irq
subsystem into a more generic library. Interrupts aren't the only
resource that want to spread across CPUs. For example, blk-mq has it's
own implementation to for polled queues, so I think a non-irq specific
implementation would be a nice addition to the kernel lib.