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SubjectRe: perf events ring buffer memory barrier on powerpc
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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