Every time synthesize instruction sample, the last branch recording will be reset. This is fine if the instruction period is big enough, for example if use the option '--itrace=i100000', the last branch array is reset for every sample with 100000 instructions per period; before generate the next instruction sample, there has the sufficient packets coming to fill the 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 the last branch array is almost empty for new instruction sample by frequently resetting.
To allow the last branches to work properly for any instruction periods, this patch avoids to reset the last branch 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; other cases can keep recording last branches for continuous instruction samples.
Signed-off-by: Leo Yan leo.yan@linaro.org --- 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 3dd5ba34a2c2..3e28462609e7 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", ret);
- if (etm->synth_opts.last_branch) - cs_etm__reset_last_branch_rb(tidq); - return ret; }
@@ -1488,6 +1485,10 @@ 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; }