linux-kernel - Re: [PATCH 4/4][RFC v2] x86/apic: Spread the vectors by choosing the idlest CPU

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Message-ID: <alpine.DEB.2.20.1709070755300.2433@nanos>
Date:   Thu, 7 Sep 2017 07:59:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dan Williams <dan.j.williams@...el.com>
cc:     Christoph Hellwig <hch@....de>, Yu Chen <yu.c.chen@...el.com>,
        X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Rui Zhang <rui.zhang@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [PATCH 4/4][RFC v2] x86/apic: Spread the vectors by choosing
 the idlest CPU

On Wed, 6 Sep 2017, Dan Williams wrote:

> On Tue, Sep 5, 2017 at 11:15 PM, Christoph Hellwig <hch@....de> wrote:
> > On Wed, Sep 06, 2017 at 12:13:38PM +0800, Yu Chen wrote:
> >> I agree, the driver could be rewritten, but it might take some time, so
> >> meanwhile I'm looking at also other possible optimization.
> >
> > Which driver are we talking about anyway?  Let's start looking at it
> > and fix the issue there.
> 
> As far as I understand, it's already fixed there:
> 
> commit 7c9ae7f053e9e896c24fd23595ba369a5fe322e1

-ENOSUCHCOMMIT

> Author: Carolyn Wyborny <carolyn.wyborny@...el.com>
> Date:   Tue Jun 20 15:16:53 2017 -0700
> 
>     i40e: Fix for trace found with S4 state
> 
>     This patch fixes a problem found in systems when entering
>     S4 state.  This patch fixes the problem by ensuring that
>     the misc vector's IRQ is disabled as well.  Without this
>     patch a stack trace can be seen upon entering S4 state.
> 
> However this seems like something that should be handled generically
> in the irq-core especially since commit c5cb83bb337c
> "genirq/cpuhotplug: Handle managed IRQs on CPU hotplug" was headed in
> that direction. It's otherwise non-obvious when a driver needs to
> release and re-acquire interrupts or be reworked to use managed
> interrupts.

There are two problems here:

1) The driver allocates 300 interrupts and uses exactly 8 randomly chosen
   ones.

2) It's not using the managed affinity mechanics, so the interrupts cannot
   be sanely handled by the kernel, neither affinity wise nor at hotplug
   time.

Thanks,

	tglx