[PATCH] coresight: Don't immediately close events that are run on invalid CPU/sink combos
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(-)
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;
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.
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
On 21/09/2021 16:17, Mathieu Poirier wrote:
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
PS: This is for coresight driver, I can pick this up. Otherwise,
Reviewed-by: Suzuki K Poulose suzuki.poulose@arm.com
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.
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
On Tue, Sep 21, 2021 at 05:22:23PM +0100, Suzuki K Poulose wrote:
On 21/09/2021 16:17, Mathieu Poirier wrote:
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
PS: This is for coresight driver, I can pick this up. Otherwise,
As yes, silly me... Sure, please add it to the tree.
Reviewed-by: Suzuki K Poulose suzuki.poulose@arm.com
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.
goto fail_end_stop;
goto out;@@ -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
On 21/09/2021 14:02, 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(-)
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.
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;
Hi James,
I think this problematic. The "out" label is reached from the "failed" path. So, we would reset the STOPPED state. I think we should simply return when we reach the "fail" label.
Please could you resend this patch with the changes.
Kind regards Suzuki
On 22/09/2021 10:24, Suzuki K Poulose wrote:
On 21/09/2021 14:02, James Clark wrote:
[...]
- 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;
Hi James,
I think this problematic. The "out" label is reached from the "failed" path. So, we would reset the STOPPED state. I think we should simply return when we reach the "fail" label.
Please could you resend this patch with the changes.
Kind regards Suzuki
Oops yes I missed that, I've resubmitted. It probably would have just about worked because from my testing it seems like the event isn't re-enabled if perf_aux_output_end() is called from start regardless of the STOPPED/RUNNING state.
Thanks James
-
James Clark -
Mathieu Poirier -
Suzuki K Poulose