On 10/29, Peter Zijlstra wrote: > > On Tue, Oct 29, 2013 at 11:30:57AM +0100, Peter Zijlstra wrote: > > @@ -154,9 +175,11 @@ int perf_output_begin(struct perf_output > > * Userspace could choose to issue a mb() before updating the > > * tail pointer. So that all reads will be completed before the > > * write is issued. > > + * > > + * See perf_output_put_handle(). > > */ > > tail = ACCESS_ONCE(rb->user_page->data_tail); > > - smp_rmb(); > > + smp_mb(); > > offset = head = local_read(&rb->head); > > head += size; > > if (unlikely(!perf_output_space(rb, tail, offset, head))) > > That said; it would be very nice to be able to remove this barrier. This > is in every event write path :/
Yes.. And I'm afraid very much that I simply confused you. Perhaps Victor is right and we do not need this mb(). So I am waiting for the end of this story too. And btw I do not understand why we need it (or smp_rmb) right after ACCESS_ONCE(data_tail). Oleg. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
