linux-kernel - Re: [GIT pull] irq updates for 4.13

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Date:   Wed, 5 Jul 2017 17:14:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>,
        Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [GIT pull] irq updates for 4.13

On Mon, Jul 03, 2017 at 05:00:03PM -0700, Linus Torvalds wrote:
> I'm not at all understanding why that second commit came in through
> the irq tree at all, in fact. Very annoying. Why was that not sent
> through the block tree? It doesn't seem to have anything fundamentally
> to do with irqs, really: it's a driver CPU choice for irq chocie.

It depends on a major IRQ layer rework, and it had at that time no
clash with the block tree at all.  That's why I suggested to Thomas
and Jens that we should take it through the irq code.  Then Max'
code showed up last minute and wrecked that plan, and no one noticed
in time.  Blame it on me for not noticing this in time.

> Anyway, I absolutely detested that code, and the obvious resolution
> was too disgusting to live. So I did an evil merge and moved some
> things around in the merge to make it at least not cause me to dig my
> eyes out.
> 
> But I'd like people to look at that - not so much due to the evil
> merge itself (but check that too, by any means), but just because the
> code seems fundamentally broken for the hotplug case. We end up
> picking a possible metric shit-ton of CPU's for queue 0, if they were
> "possible but not online".

I think this code also needs to move over to cpu_possible instead
of cpu_online to match what we did for the MSI-X based mapping.  But
I'll need a little more coffee and get back into it.