Messages in this thread | | | Date | Tue, 21 Sep 2021 09:17:21 -0600 | From | Mathieu Poirier <> | Subject | Re: [PATCH] coresight: Don't immediately close events that are run on invalid CPU/sink combos |
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On Tue, Sep 21, 2021 at 02:02:31PM +0100, 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 > > Signed-off-by: James Clark <james.clark@arm.com> > --- > .../hwtracing/coresight/coresight-etm-perf.c | 27 +++++++++++++++---- > 1 file changed, 22 insertions(+), 5 deletions(-)
Very interesting corner case - and I like your solution. Arnaldo, please consider.
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c > index 8ebd728d3a80..79346f0f0e0b 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: > @@ -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; > > -- > 2.28.0 >
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