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Peter Anvin" , Mathieu Poirier , Mike Leach , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v4 02/11] coresight: tmc-etr: Add barrier after updating AUX ring buffer Message-ID: <20210712105431.GA704210@leoy-ThinkPad-X240s> References: <20210711104105.505728-1-leo.yan@linaro.org> <20210711104105.505728-3-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Hi Suzuki, On Mon, Jul 12, 2021 at 11:40:12AM +0100, Suzuki Kuruppassery Poulose wrote: > On 11/07/2021 11:40, Leo Yan wrote: > > Since a memory barrier is required between AUX trace data store and > > aux_head store, and the AUX trace data is filled with memcpy(), it's > > sufficient to use smp_wmb() so can ensure the trace data is visible > > prior to updating aux_head. > > > > Signed-off-by: Leo Yan > > --- > > drivers/hwtracing/coresight/coresight-tmc-etr.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c > > index acdb59e0e661..713205db15a1 100644 > > --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c > > +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c > > @@ -1563,6 +1563,14 @@ tmc_update_etr_buffer(struct coresight_device *csdev, > > */ > > if (etr_perf->snapshot) > > handle->head += size; > > + > > + /* > > + * It requires the ordering between the AUX trace data and aux_head > > + * store, below smp_wmb() ensures the AUX trace data is visible prior > > + * to updating aux_head. > > + */ > > Please could we reword this a bit, something like : > > /* > * Ensure that the AUX trace data is visible before the aux_head > * is updated via perf_aux_output_end(), as expected by the > * perf ring buffer. > */ Will refine with this in next spin. Thanks for review! > > + smp_wmb(); > > + > > Reviewed-by: Suzuki K Poulose