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[68.147.8.254]) by smtp.gmail.com with ESMTPSA id g136sm19265654pfb.154.2018.12.10.14.48.17 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Dec 2018 14:48:17 -0800 (PST) Date: Mon, 10 Dec 2018 15:48:15 -0700 From: Mathieu Poirier To: Leo Yan Cc: Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Coresight ML , Mike Leach , Robert Walker Subject: Re: [PATCH v2 2/6] perf cs-etm: Avoid stale branch samples when flush packet Message-ID: <20181210224815.GA12152@xps15> References: <1544431981-24144-1-git-send-email-leo.yan@linaro.org> <1544431981-24144-3-git-send-email-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1544431981-24144-3-git-send-email-leo.yan@linaro.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 10, 2018 at 04:52:57PM +0800, Leo Yan wrote: > At the end of trace buffer handling, function cs_etm__flush() is invoked > to flush any remaining branch stack entries. As a side effect, it also > generates branch sample, because the 'etmq->packet' doesn't contains any > new coming packet but point to one stale packet after packets swapping, > so it wrongly makes synthesize branch samples with stale packet info. > > We could review below detailed flow which causes issue: > > Packet1: start_addr=0xffff000008b1fbf0 end_addr=0xffff000008b1fbfc > Packet2: start_addr=0xffff000008b1fb5c end_addr=0xffff000008b1fb6c > > step 1: cs_etm__sample(): > sample: ip=(0xffff000008b1fbfc-4) addr=0xffff000008b1fb5c > > step 2: flush packet in cs_etm__run_decoder(): > cs_etm__run_decoder() > `-> err = cs_etm__flush(etmq, false); > sample: ip=(0xffff000008b1fb6c-4) addr=0xffff000008b1fbf0 > > Packet1 and packet2 are two continuous packets, when packet2 is the new > coming packet, cs_etm__sample() generates branch sample for these two > packets and use [packet1::end_addr - 4 => packet2::start_addr] as branch > jump flow, thus we can see the first generated branch sample in step 1. > At the end of cs_etm__sample() it swaps packets so 'etm->prev_packet'= > packet2 and 'etm->packet'=packet1, so far it's okay for branch sample. > > If packet2 is the last one packet in trace buffer, even there have no > any new coming packet, cs_etm__run_decoder() invokes cs_etm__flush() to > flush branch stack entries as expected, but it also generates branch > samples by taking 'etm->packet' as a new coming packet, thus the branch > jump flow is as [packet2::end_addr - 4 => packet1::start_addr]; this > is the second sample which is generated in step 2. So actually the > second sample is a stale sample and we should not generate it. > > This patch introduces a new function cs_etm__end_block(), at the end of > trace block this function is invoked to only flush branch stack entries > and thus can avoid to generate branch sample for stale packet. > > Cc: Mathieu Poirier > Cc: Mike Leach > Cc: Robert Walker > Signed-off-by: Leo Yan > --- > tools/perf/util/cs-etm.c | 35 ++++++++++++++++++++++++++++++++++- > 1 file changed, 34 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > index 789707b..ffc4fe5 100644 > --- a/tools/perf/util/cs-etm.c > +++ b/tools/perf/util/cs-etm.c > @@ -1055,6 +1055,39 @@ static int cs_etm__flush(struct cs_etm_queue *etmq) > return err; > } > > +static int cs_etm__end_block(struct cs_etm_queue *etmq) > +{ > + int err; > + > + /* > + * It has no new packet coming and 'etmq->packet' contains the stale > + * packet which was set at the previous time with packets swapping; > + * so skip to generate branch sample to avoid stale packet. > + * > + * For this case only flush branch stack and generate a last branch > + * event for the branches left in the circular buffer at the end of > + * the trace. > + */ > + if (etmq->etm->synth_opts.last_branch && > + etmq->prev_packet->sample_type == CS_ETM_RANGE) { > + /* > + * Use the address of the end of the last reported execution > + * range. > + */ > + u64 addr = cs_etm__last_executed_instr(etmq->prev_packet); > + > + err = cs_etm__synth_instruction_sample( > + etmq, addr, > + etmq->period_instructions); > + if (err) > + return err; > + > + etmq->period_instructions = 0; > + } > + > + return 0; > +} > + > static int cs_etm__run_decoder(struct cs_etm_queue *etmq) > { > struct cs_etm_auxtrace *etm = etmq->etm; > @@ -1137,7 +1170,7 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq) > > if (err == 0) > /* Flush any remaining branch stack entries */ > - err = cs_etm__flush(etmq); > + err = cs_etm__end_block(etmq); > } > > return err; Reviewed-by: Mathieu Poirier > -- > 2.7.4 >