Messages in this thread | | | Date | Tue, 29 Oct 2013 11:35:26 +0100 | From | Peter Zijlstra <> | Subject | Re: perf events ring buffer memory barrier on powerpc |
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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 :/
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