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;