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

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Message-ID: <CAPcyv4igaPQ1V0QxDaXbpfecNuhUGS0Rx-povbyi5HY_Y9OBSg@mail.gmail.com>
Date:   Wed, 6 Sep 2017 10:46:17 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Yu Chen <yu.c.chen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, 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>
Subject: Re: [PATCH 4/4][RFC v2] x86/apic: Spread the vectors by choosing the
 idlest CPU

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
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.