linux-kernel - Re: [PATCH 03/10] smp,cpumask: introduce on_each_cpu_cond

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Date:   Sun, 29 Jul 2018 12:56:46 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Rik van Riel <riel@...riel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Dave Hansen <dave.hansen@...el.com>, will.daecon@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 03/10] smp,cpumask: introduce on_each_cpu_cond_mask

On Sun, Jul 29, 2018 at 11:55 AM Andy Lutomirski <luto@...capital.net> wrote:
> > On Jul 29, 2018, at 10:51 AM, Rik van Riel <riel@...riel.com> wrote:
> >
> > This seems to result in systems with ->has_wbinvd_exit
> > only calling wbinvd_ipi on OTHER CPUs, and not on the
> > CPU where the guest exited with wbinvd?
> >
> > This seems unintended.
> >
> > I guess looking into on_each_cpu_mask might be a little
> > higher priority than waiting until the next Outreachy
> > season :)
>
> The right approach might be a tree wise rename from smp_call_... to on_other_cpus_mask() it similar. The current naming and semantics are extremely confusing.

Ugh.

Renaming might be worth it, but at least one issue is that we are
simply not very consistent.

For example. smp_call_function_many() does indeed explicitly ignore
the current CPU.

But smp_call_function_any() (one "m" less) does _not_ ignore the
current CPU, and in fact prefers it.

So it's not that smp_call_... should *generally* be renamed. Only some
of the cases might be worth renaming.

And just a "rename and forget" isn't really great. As Rik's example
shows, existing users should be checked too..

                    Linus