| Message ID | 20210922125144.133872-2-james.clark@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Don't immediately close events that are run on invalid CPU/sink combos | expand |
On 22/09/2021 13:51, James Clark wrote: > When a traced process runs on a CPU that can't reach the selected sink, > the event will be stopped with PERF_HES_STOPPED. This means that even if > the process migrates to a valid CPU, tracing will not resume. > > This can be reproduced (on N1SDP) by using taskset to start the process > on CPU 0, and then switching it to CPU 2 (ETF 1 is only reachable from > CPU 2): > > taskset --cpu-list 0 ./perf record -e cs_etm/@tmc_etf1/ --per-thread -- taskset --cpu-list 2 ls > > This produces a single 0 length AUX record, and then no more trace: > > 0x3c8 [0x30]: PERF_RECORD_AUX offset: 0 size: 0 flags: 0x1 [T] > > After the fix, the same command produces normal AUX records. The perf > self test "89: Check Arm CoreSight trace data recording and synthesized > samples" no longer fails intermittently. This was because the taskset in > the test is after the fork, so there is a period where the task is > scheduled on a random CPU rather than forced to a valid one. > > Specifically selecting an invalid CPU will still result in a failure to > open the event because it will never produce trace: > > ./perf record -C 2 -e cs_etm/@tmc_etf0/ > failed to mmap with 12 (Cannot allocate memory) > > The only scenario that has changed is if the CPU mask has a valid CPU > sink combo in it. > > Testing > ======= > > * Coresight self test passes consistently: > ./perf test Coresight > > * CPU wide mode still produces trace: > ./perf record -e cs_etm// -a > > * Invalid -C options still fail to open: > ./perf record -C 2,3 -e cs_etm/@tmc_etf0/ > failed to mmap with 12 (Cannot allocate memory) > > * Migrating a task to a valid sink/CPU now produces trace: > taskset --cpu-list 0 ./perf record -e cs_etm/@tmc_etf1/ --per-thread -- taskset --cpu-list 2 ls > > * If the task remains on an invalid CPU, no trace is emitted: > taskset --cpu-list 0 ./perf record -e cs_etm/@tmc_etf1/ --per-thread -- ls > > Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org> > Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> > Signed-off-by: James Clark <james.clark@arm.com> Thanks James, I have queued this. Suzuki
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c index 8ebd728d3a80..3bce1ec4c4bf 100644 --- a/drivers/hwtracing/coresight/coresight-etm-perf.c +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c @@ -452,9 +452,14 @@ static void etm_event_start(struct perf_event *event, int flags) * sink from this ETM. We can't do much in this case if * the sink was specified or hinted to the driver. For * now, simply don't record anything on this ETM. + * + * As such we pretend that everything is fine, and let + * it continue without actually tracing. The event could + * continue tracing when it moves to a CPU where it is + * reachable to a sink. */ if (!cpumask_test_cpu(cpu, &event_data->mask)) - goto fail_end_stop; + goto out; path = etm_event_cpu_path(event_data, cpu); /* We need a sink, no need to continue without one */ @@ -466,16 +471,15 @@ static void etm_event_start(struct perf_event *event, int flags) if (coresight_enable_path(path, CS_MODE_PERF, handle)) goto fail_end_stop; - /* Tell the perf core the event is alive */ - event->hw.state = 0; - /* Finally enable the tracer */ if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF)) goto fail_disable_path; +out: + /* Tell the perf core the event is alive */ + event->hw.state = 0; /* Save the event_data for this ETM */ ctxt->event_data = event_data; -out: return; fail_disable_path: @@ -485,7 +489,7 @@ static void etm_event_start(struct perf_event *event, int flags) perf_aux_output_end(handle, 0); fail: event->hw.state = PERF_HES_STOPPED; - goto out; + return; } static void etm_event_stop(struct perf_event *event, int mode) @@ -517,6 +521,19 @@ static void etm_event_stop(struct perf_event *event, int mode) if (WARN_ON(!event_data)) return; + /* + * Check if this ETM was allowed to trace, as decided at + * etm_setup_aux(). If it wasn't allowed to trace, then + * nothing needs to be torn down other than outputting a + * zero sized record. + */ + if (handle->event && (mode & PERF_EF_UPDATE) && + !cpumask_test_cpu(cpu, &event_data->mask)) { + event->hw.state = PERF_HES_STOPPED; + perf_aux_output_end(handle, 0); + return; + } + if (!csdev) return;