On 2023/9/15 20:53, Suzuki K Poulose wrote:
> On 14/09/2023 12:22, Yicong Yang wrote:
>> From: Junhao He <hejunhao3@xxxxxxxxxx>
>>
>> When start trace with perf option "-C $cpu" and immediately stop it
>> with SIGTERM or others, the perf core will invoke pmu::read() while
>> the driver doesn't implement it. Add a dummy pmu::read() to avoid
>> any issues.
>
> What issues are we talking about here ? Shouldn't the core perf
> skip the call, if pmu::read() is not available ?
>
Actually no, the core doesn't check it. So I think that's why some PMUs
like SPE implements a dummy pmu::read() callback. Otherwise we'll
dereference a NULL pointer.
Currently we only met this on emulated platforms with very slow CPUs,
follow the instructions in the commit above.
> Suzuki
>
>>
>> Signed-off-by: Junhao He <hejunhao3@xxxxxxxxxx>
>> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
>> Acked-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>> ---
>> drivers/hwtracing/ptt/hisi_ptt.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c
>> index 62a444f5228e..c1b5fd2b8974 100644
>> --- a/drivers/hwtracing/ptt/hisi_ptt.c
>> +++ b/drivers/hwtracing/ptt/hisi_ptt.c
>> @@ -1184,6 +1184,10 @@ static void hisi_ptt_pmu_del(struct perf_event *event, int flags)
>> hisi_ptt_pmu_stop(event, PERF_EF_UPDATE);
>> }
>> +static void hisi_ptt_pmu_read(struct perf_event *event)
>> +{
>> +}
>> +
>> static void hisi_ptt_remove_cpuhp_instance(void *hotplug_node)
>> {
>> cpuhp_state_remove_instance_nocalls(hisi_ptt_pmu_online, hotplug_node);
>> @@ -1227,6 +1231,7 @@ static int hisi_ptt_register_pmu(struct hisi_ptt *hisi_ptt)
>> .stop = hisi_ptt_pmu_stop,
>> .add = hisi_ptt_pmu_add,
>> .del = hisi_ptt_pmu_del,
>> + .read = hisi_ptt_pmu_read,
>> };
>> reg = readl(hisi_ptt->iobase + HISI_PTT_LOCATION);
>
>
> .
