linux-kernel - Re: Virtually Mapped Stacks: Do not disable interrupts

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Message-ID: <CALCETrXestE8xa3K-oF-XO_jXO8L27LLD03RytX0Tw8BLHO9DQ@mail.gmail.com>
Date:   Thu, 18 May 2017 22:38:28 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Christoph Lameter <cl@...ux.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Virtually Mapped Stacks: Do not disable interrupts

On Wed, May 17, 2017 at 8:58 AM, Christoph Lameter <cl@...ux.com> wrote:
> The reason to disable interrupts seems to be to avoid switching
> to a different processor while handling per cpu data using
> individual loads and stores. If we use per cpu RMV primitives
> we will not have to disable interrupts.

I like this, except that those primitives can be quite expensive, I
think, and they're being called in a loop.  What if you first did a
this_cpu_read() to see if the value in the cache slot might be useful
before doing the heavyweight exchange?

--Andy