[PATCH v1 1/4] perf cs-etm: Continuously record last branches

From: Leo Yan
Date: Thu Oct 24 2019 - 11:15:12 EST

Every time synthesize instruction sample, the last branches recording
will be reset. This would be fine if the instruction period is big
enough, for example if we use the option '--itrace=i100000', the last
branch array is reset for every instruction sample (10000 instructions
per period); before generate the next instruction sample, there has the
enough packets coming to fill last branch array. On the other hand,
if set a very small period, the packets will be significantly reduced
between two continuous instruction samples, thus if the last branch
array is reset for the previous instruction sample, it's almost empty
for the next instruction sample.

To allow the last branches to work for any instruction periods, this
patch avoids to reset the last branches for every instruction sample
and only reset it when flush the trace data. The last branches will
be reset only for two cases, one is for trace starting, another case
is for discontinuous trace; thus it can continuously record last

Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
tools/perf/util/cs-etm.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index f5f855fff412..8be6d010ae84 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -1153,9 +1153,6 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
"CS ETM Trace: failed to deliver instruction event, error %d\n",

- if (etm->synth_opts.last_branch)
- cs_etm__reset_last_branch_rb(tidq);
return ret;

@@ -1486,6 +1483,10 @@ static int cs_etm__flush(struct cs_etm_queue *etmq,
tidq->prev_packet = tmp;

+ /* Reset last branches after flush the trace */
+ if (etm->synth_opts.last_branch)
+ cs_etm__reset_last_branch_rb(tidq);
return err;