linux-kernel - Re: [PATCH v3 2/5] perf cs-etm: Continuously record last branch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 5 Feb 2020 16:01:11 +0000
From:   Mike Leach <mike.leach@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org,
        Robert Walker <robert.walker@....com>,
        Coresight ML <coresight@...ts.linaro.org>
Subject: Re: [PATCH v3 2/5] perf cs-etm: Continuously record last branch

On Mon, 3 Feb 2020 at 01:52, Leo Yan <leo.yan@...aro.org> wrote:
>
> 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@...aro.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;
>  }
>
> --
> 2.17.1
>

Reviewed by: Mike Leach <mike.leach@...aro.org>
-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK