netdev - Re: [Patch v4 1/3] lib: Restrict cpumask_local

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Date:   Fri, 30 Apr 2021 09:10:40 -0400
From:   Nitesh Lal <nilal@...hat.com>
To:     Jesse Brandeburg <jesse.brandeburg@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "frederic@...nel.org" <frederic@...nel.org>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>, abelits@...vell.com,
        Robin Murphy <robin.murphy@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "rppt@...ux.vnet.ibm.com" <rppt@...ux.vnet.ibm.com>,
        "jinyuqi@...wei.com" <jinyuqi@...wei.com>,
        "zhangshaokun@...ilicon.com" <zhangshaokun@...ilicon.com>,
        netdev@...r.kernel.org, chris.friesen@...driver.com
Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs

On Thu, Apr 29, 2021 at 9:48 PM Jesse Brandeburg
<jesse.brandeburg@...el.com> wrote:
>
> Nitesh Lal wrote:
>
> > @Jesse do you think the Part-1 findings explain the behavior that you have
> > observed in the past?
> >
> > Also, let me know if there are any suggestions or experiments to try here.
>
> Wow Nitesh, nice work! That's quite a bit of spelunking you had to do
> there!
>
> Your results that show the older kernels with ranged affinity issues is
> consistent with what I remember from that time, and the original
> problem.

That's nice.

>
> I'm glad to see that a) Thomas fixed the kernel to even do better than
> ranged affinity masks, and that b) if you revert my patch, the new
> behavior is better and still maintains the fix from a).

Right, the interrupts are naturally spread now.

>
> For me this explains the whole picture and makes me feel comfortable
> with the patch that reverts the initial affinity mask (that also
> introduces a subtle bug with the reserved CPUs that I believe you've
> noted already).
>

Thank you for confirming!

--
Nitesh