* H. Peter Anvin <h...@zytor.com> wrote:
> On 12/19/2013 08:21 AM, Peter Zijlstra wrote:
> >
> > What's that mb for?
> >
>
> It already exists in mwait_idle_with_hints(); I just moved it into
> this common function. It is a bit odd, I have to admit; it seems
> like it should be *before* the monitor (and possibly we should have
> one after the CLFLUSH as well?)
Yes, I think we need a barrier before the CLFLUSH, because according
to my reading of the Intel documentation CLFLUSH has no implicit
ordering so it might get reordered with the store to ->flags in
current_set_polling_and_test(), which might result in spurious wakeup
problems again.
(And CLFLUSH is a store in a sense, so special in that the regular
ordering for stores does not apply.)
Likewise, having a barrier before the MONITOR looks sensible as well.
Having it _after_ monitor looks weird and is probably wrong. [It might
have been the effects of someone seeing the spurious wakeup problems
with realizing the true source, or so.]
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
