Re: [PATCH V6 21/26] coresight: etm-perf: new PMU driver for ETM tracers

Mathieu Poirier
2015-12-11T21:18:12Z

On 11 December 2015 at 08:18, Alexander Shishkin
<alexander.shishkin@linux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@linaro.org> writes:
>
>> +static void etm_event_start(struct perf_event *event, int flags)
>> +{
>> + int cpu = smp_processor_id();
>> + struct etm_cpu_data *cpu_data;
>> + struct etm_event_data *event_data;
>> + struct perf_output_handle *handle = this_cpu_ptr(&ctx_handle);
>> + struct coresight_device *sink, *csdev = per_cpu(csdev_src, cpu);
>> +
>> + if (!csdev)
>> + goto fail;
>> +
>> + /*
>> + * Deal with the ring buffer API and get a handle on the
>> + * session's information.
>> + */
>> + event_data = perf_aux_output_begin(handle, event);
>> + if (WARN_ON_ONCE(!event_data))
>> + goto fail;
>
> Hmm, perf_aux_output_begin() returning NULL is not WARN-worthy and is
> actually a normal situation, for example, if the buffer is not
> configured yet (which like I suggested in the other email should be a
> separate thing from the *event* configuration).
>
> perf_aux_output_begin() will also return NULL if there's no room in the
> buffer.

You are correct - I'll revise this.

>
> Regards,
> --
> Alex