linux-kernel - Re: [PATCH RFC cpumask 4/5] cpumask: Add "last" alias for cpu list specifications

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Date:   Thu, 7 Jan 2021 15:18:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     paulmck@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-team@...com, Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RFC cpumask 4/5] cpumask: Add "last" alias for cpu list
 specifications

On Wed, Jan 06, 2021 at 01:16:50PM -0800, Yury Norov wrote:
> On Wed, Jan 6, 2021 at 1:50 AM Peter Zijlstra <peterz@...radead.org> wrote:

> > Aside from the comments Yury made, on how all this is better in
> > bitmap_parselist(), how about doing s/last/N/ here? For me something
> > like: "4-N" reads much saner than "4-last".
> >
> > Also, it might make sense to teach all this about core/node topology,
> > but that's going to be messy. Imagine something like "Core1-CoreN" or
> > "Nore1-NodeN" to mean the mask all/{Core,Node}0.
> 
> If you just want to teach bitmap_parselist() to "s/Core0/0-4",  I think
> it's doable if we add a hook to a proper subsystem in bitmap_parselist().
> 
> > And that is another feature that seems to be missing from parselist,
> > all/except.
> 
> We already support groups in a range. I think it partially covers the
> proposed all/except.
> 
> Can you share examples on what you miss?

The obvious one is the "all/Core0" example above, which would be
equivalent to "Core1-CoreN".

Another case that I don't think we can do today is something like, give
me SMT0 of each core.

I don't really see the use of the ranges thing, CPU enumeration just
isn't sane like that. Also, I should really add that randomization pass
to the CPU enumeration :-)