Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs

From: Nitesh Lal
Date: Fri Apr 30 2021 - 09:11:01 EST

On Thu, Apr 29, 2021 at 9:48 PM Jesse Brandeburg
<jesse.brandeburg@xxxxxxxxx> 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!