linux-kernel - Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets

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Date:   Tue, 22 May 2018 17:52:49 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Robert Walker <robert.walker@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tor Jeremiassen <tor@...com>,
        mike.leach@...aro.org, kim.phillips@....com,
        coresight@...ts.linaro.org, Mike Leach <mike.leach@....com>
Subject: Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets

On Tue, May 22, 2018 at 04:39:20PM +0800, Leo Yan wrote:

[...]

Rather than the patch I posted in my previous email, I think below new
patch is more reasonable for me.

In the below change, 'etmq->prev_packet' is only used to store the
previous CS_ETM_RANGE packet, we don't need to save CS_ETM_TRACE_ON
packet into 'etmq->prev_packet'.

On the other hand, cs_etm__flush() can use 'etmq->period_instructions'
to indicate if need to generate instruction sample or not.  If it's
non-zero, then generate instruction sample and
'etmq->period_instructions' will be cleared; so next time if there
have more tracing CS_ETM_TRACE_ON packet, it can skip to generate
instruction sample due 'etmq->period_instructions' is zero.

How about you think for this?

Thanks,
Leo Yan


diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 822ba91..dd354ad 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -495,6 +495,13 @@ static inline void cs_etm__reset_last_branch_rb(struct cs_etm_queue *etmq)
 static inline u64 cs_etm__last_executed_instr(struct cs_etm_packet *packet)
 {
 	/*
+	 * The packet is the start tracing packet if the end_addr is zero,
+	 * returns 0 for this case.
+	 */
+	if (!packet->end_addr)
+		return 0;
+
+	/*
 	 * The packet records the execution range with an exclusive end address
 	 *
 	 * A64 instructions are constant size, so the last executed
@@ -897,13 +904,27 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
 		etmq->period_instructions = instrs_over;
 	}
 
-	if (etm->sample_branches &&
-	    etmq->prev_packet &&
-	    etmq->prev_packet->sample_type == CS_ETM_RANGE &&
-	    etmq->prev_packet->last_instr_taken_branch) {
-		ret = cs_etm__synth_branch_sample(etmq);
-		if (ret)
-			return ret;
+	if (etm->sample_branches && etmq->prev_packet) {
+		bool generate_sample = false;
+
+		/* Generate sample for start tracing packet */
+		if (etmq->prev_packet->sample_type == 0)
+			generate_sample = true;
+
+		/* Generate sample for exception packet */
+		if (etmq->prev_packet->exc == true)
+			generate_sample = true;
+
+		/* Generate sample for normal branch packet */
+		if (etmq->prev_packet->sample_type == CS_ETM_RANGE &&
+		    etmq->prev_packet->last_instr_taken_branch)
+			generate_sample = true;
+
+		if (generate_sample) {
+			ret = cs_etm__synth_branch_sample(etmq);
+			if (ret)
+				return ret;
+		}
 	}
 
 	if (etm->sample_branches || etm->synth_opts.last_branch) {
@@ -922,11 +943,12 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
 static int cs_etm__flush(struct cs_etm_queue *etmq)
 {
 	int err = 0;
-	struct cs_etm_packet *tmp;
 
 	if (etmq->etm->synth_opts.last_branch &&
 	    etmq->prev_packet &&
-	    etmq->prev_packet->sample_type == CS_ETM_RANGE) {
+	    etmq->prev_packet->sample_type == CS_ETM_RANGE &&
+	    etmq->period_instructions) {
+
 		/*
 		 * Generate a last branch event for the branches left in the
 		 * circular buffer at the end of the trace.
@@ -940,14 +962,6 @@ static int cs_etm__flush(struct cs_etm_queue *etmq)
 			etmq, addr,
 			etmq->period_instructions);
 		etmq->period_instructions = 0;
-
-		/*
-		 * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
-		 * the next incoming packet.
-		 */
-		tmp = etmq->packet;
-		etmq->packet = etmq->prev_packet;
-		etmq->prev_packet = tmp;
 	}
 
 	return err;
-- 
2.7.4