* Davidlohr Bueso <d...@stgolabs.net> wrote:
> On Fri, 05 Feb 2016, Ingo Molnar wrote:
>
> >So I too didn't understand that sentence at first, because the capitalization
> >really throws off quick parsing of that comment, as 'MB' ususally denotes
> >megabytes.
>
> Sure, fair enough.
>
> >
> >So please change it to "mb(); (A)" or so - and I think all of these comments
> >should be changed to use a standard API name for the barrier they imply, as
> >the
> >head of futex.c does:
> >
> >* waiters++; (a)
> >* mb(); (A) <-- paired with -.
> >* |
> >* lock(hash_bucket(futex)); |
> >* |
> >* uval = *futex; |
> >* | *futex = newval;
> >* | sys_futex(WAKE, futex);
> >* | futex_wake(futex);
> >* |
> >* `-------> mb(); (B)
> >
> >Btw., pedantic: shouldn't that be smp_mb()? Futexes don't operate on IO
> >spaces, so
> >on UP they only need compiler barriers.
>
> Right, but we do in fact use smp barriers in this cases in the real code,
> that
> mb() is just in the comments, I guess it would be desirable to change it to
> smp_mb nonetheless.
>
> However, could these changes be in a followup? Mainly because the barrier B
> references will be updated across all futex.c... unless there are still
> concerns
> about this particular patch, of course.
How about doing it first in a preparatory patch? So that reviews of patches
actually making substantial changes don't get derailed by hard to read comments
and so.
Thanks,
Ingo
