Messages in this thread | | | Date | Thu, 19 Oct 2023 11:38:57 +0100 | Subject | Re: [PATCH v1 2/2] perf cs-etm: Enable itrace option 'T' | From | James Clark <> |
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On 14/10/2023 08:45, Leo Yan wrote: > Prior to Armv8.4, the feature FEAT_TRF is not supported by Arm CPUs. > Consequently, the sysfs node 'ts_source' will not be set as 1 by the > CoreSight ETM driver. On the other hand, the perf tool relies on the > 'ts_source' node to determine whether the kernel timestamp is traced. > Since the 'ts_source' is not set for Arm CPUs prior to Armv8.4, > platforms in this case cannot utilize the traced timestamp as the kernel > time. > > This patch enables the 'T' itrace option, which forcibly utilizes the > traced timestamp as the kernel time. If users are aware that their > working platform's Arm CoreSight shares the same counter with the kernel > time, they can specify 'T' option to decode the traced timestamp as the > kernel time. > > An usage example is: > > # perf record -e cs_etm// -- test_program > # perf script --itrace=i10ibT > # perf report --itrace=i10ibT > > Signed-off-by: Leo Yan <leo.yan@linaro.org> > --- > tools/perf/util/cs-etm.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > index 9729d006550d..4a37fdeb1795 100644 > --- a/tools/perf/util/cs-etm.c > +++ b/tools/perf/util/cs-etm.c > @@ -3322,12 +3322,27 @@ int cs_etm__process_auxtrace_info_full(union perf_event *event, > etm->metadata = metadata; > etm->auxtrace_type = auxtrace_info->type; > > - /* Use virtual timestamps if all ETMs report ts_source = 1 */ > - etm->has_virtual_ts = cs_etm__has_virtual_ts(metadata, num_cpu); > + if (etm->synth_opts.use_timestamp) > + /* > + * Prior to Armv8.4, Arm CPUs don't support FEAT_TRF feature, > + * therefore the decoder cannot know if the timestamp trace is > + * same with the kernel time. > + * > + * If a user has knowledge for the working platform and can > + * specify itrace option 'T' to tell decoder to forcely use the > + * traced timestamp as the kernel time. > + */ > + etm->has_virtual_ts = true; > + else > + /* Use virtual timestamps if all ETMs report ts_source = 1 */ > + etm->has_virtual_ts = cs_etm__has_virtual_ts(metadata, num_cpu); > > if (!etm->has_virtual_ts) > ui__warning("Virtual timestamps are not enabled, or not supported by the traced system.\n" > - "The time field of the samples will not be set accurately.\n\n"); > + "The time field of the samples will not be set accurately.\n" > + "For Arm CPUs prior to Armv8.4 or without support FEAT_TRF,\n" > + "you can specify the itrace option 'T' for timestamp decoding\n" > + "if the Coresight timestamp on the platform is same with the kernel time.\n\n"); > > etm->auxtrace.process_event = cs_etm__process_event; > etm->auxtrace.process_auxtrace_event = cs_etm__process_auxtrace_event;
Reviewed-by: James Clark <james.clark@arm.com>
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