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Date: Tue, 29 Oct 2013 11:35:26 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Victor Kaplansky <VICTORK@...ibm.com> Cc: Oleg Nesterov <oleg@...hat.com>, Anton Blanchard <anton@...ba.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Frederic Weisbecker <fweisbec@...il.com>, LKML <linux-kernel@...r.kernel.org>, Linux PPC dev <linuxppc-dev@...abs.org>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Michael Ellerman <michael@...erman.id.au>, Michael Neuling <mikey@...ling.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: Re: 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 :/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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