Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers

[Linus Torvalds]

On Fri, Oct 3, 2014 at 5:01 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> The real fix would appear to be to use
> "preempt_enable_no_resched_notrace()", which your patch did, but
> without the loop.

Actually, the real fix would be to not be stupid, and just make the
code do something like

>        if (likely(!preemptible()))
>                return;
>
>         __preempt_count_add(PREEMPT_ACTIVE);
>         prev_ctx = exception_enter();
>
>         __schedule();
>
>         exception_exit(prev_ctx);
>         __preempt_count_sub(PREEMPT_ACTIVE);

and *not* enable preemption around the scheduling at all. The whole
enable and then re-disable seems entirely broken, and comes from the
code using "preempt_schedule()" which doesn't work while preemption is
disabled. So don't do that then.

No?

               Linus
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