[lkml]   [2013]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: perf events ring buffer memory barrier on powerpc
Peter Zijlstra <> wrote on 10/30/2013 01:25:26 PM:

> Also, I'm not entirely sure on C, that too seems like a dependency, we
> simply cannot read the buffer @tail before we've read the tail itself,
> now can we? Similarly we cannot compare tail to head without having the
> head read completed.

No, this one we cannot omit, because our problem on consumer side is not
with @tail, which is written exclusively by consumer, but with @head.

BTW, it is why you also don't need ACCESS_ONCE() around @tail, but only
@head read.

-- Victor

 \ /
  Last update: 2013-10-30 16:21    [W:0.198 / U:6.428 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site