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    Subject[PATCH 10/23] perf cs-etm: Continuously record last branch
    Date
    From: Leo Yan <leo.yan@linaro.org>

    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>
    Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
    Reviewed-by: Mike Leach <mike.leach@linaro.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Robert Walker <robert.walker@arm.com>
    Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
    Cc: coresight ml <coresight@lists.linaro.org>
    Cc: linux-arm-kernel@lists.infradead.org
    Link: http://lore.kernel.org/lkml/20200219021811.20067-3-leo.yan@linaro.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    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 294b09cfb034..2c4156c5ed09 100644
    --- a/tools/perf/util/cs-etm.c
    +++ b/tools/perf/util/cs-etm.c
    @@ -1170,9 +1170,6 @@ 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;
    }

    @@ -1487,6 +1484,10 @@ static int cs_etm__flush(struct cs_etm_queue *etmq,
    swap_packet:
    cs_etm__packet_swap(etm, tidq);

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

    --
    2.21.1
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