Re: [PATCH v3 4/6] coresight: perf: Support AUX trace pause and resume

Hi Mike,

On Tue, Apr 01, 2025 at 01:50:52PM +0100, Mike Leach wrote:

[...]

...

static void etm_event_start(struct perf_event *event, int flags) { int cpu = smp_processor_id(); @@ -463,6 +484,14 @@ static void etm_event_start(struct perf_event *event, int flags) if (!csdev) goto fail;

Is it possible here that the first call to etm_event_start() also has the PERF_EF_RESUME flag set?

The first call has a flow below, using flag 0 but not PERF_EF_RESUME.

etm_event_add() `> etm_event_start(event, 0);

Note: for the first call, the tracer should be disabled if 'event->hw.aux_paused' is 1. This is ensured by patch 03.

Thanks, Leo

If so it looks like we need to fall through and do a "normal" start to get all the ctxt->event_data set up.

...

•   if (flags & PERF_EF_RESUME) {
  

•           if (etm_event_resume(csdev, ctxt) < 0) {
  

•                   dev_err(&csdev->dev, "Failed to resume ETM event.\n");
  

•                   goto fail;
  

•           }
  

•           return;
  

•   }
  

•   /* Have we messed up our tracking ? */
    if (WARN_ON(ctxt->event_data))
            goto fail;
  

@@ -545,6 +574,16 @@ static void etm_event_start(struct perf_event *event, int flags) return; }

+static void etm_event_pause(struct coresight_device *csdev,

•                       struct etm_ctxt *ctxt)
  

+{

•   if (!ctxt->event_data)
  

•           return;
  

•   /* Stop tracer */
  

•   coresight_pause_source(csdev);
  

+}

static void etm_event_stop(struct perf_event *event, int mode) { int cpu = smp_processor_id(); @@ -555,6 +594,9 @@ static void etm_event_stop(struct perf_event *event, int mode) struct etm_event_data *event_data; struct coresight_path *path;

•   if (mode & PERF_EF_PAUSE)
  

•           return etm_event_pause(csdev, ctxt);
  

•   /*
     * If we still have access to the event_data via handle,
     * confirm that we haven't messed up the tracking.
  

@@ -899,7 +941,8 @@ int __init etm_perf_init(void) int ret;

    etm_pmu.capabilities            = (PERF_PMU_CAP_EXCLUSIVE |

•                                      PERF_PMU_CAP_ITRACE);
  

•                                      PERF_PMU_CAP_ITRACE |
  

•                                      PERF_PMU_CAP_AUX_PAUSE);
  
    etm_pmu.attr_groups             = etm_pmu_attr_groups;
    etm_pmu.task_ctx_nr             = perf_sw_context;
  

-- 2.34.1

If the possible issue above is prevented by perf internals

Reviewed-by: Mike Leach mike.leach@linaro.org

-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK