On 7 August 2016 at 15:10, David Carrillo-Cisneros <davi...@google.com> wrote:
> Hi Nilay,
>
>>> static int perf_event_read(struct perf_event *event, bool group)
>>> {
>>> - int ret = 0;
>>> + int ret = 0, cpu_to_read;
>>>
>>> - /*
>>> - * If event is enabled and currently active on a CPU, update the
>>> - * value in the event structure:
>>> - */
>>> - if (event->state == PERF_EVENT_STATE_ACTIVE) {
>>> + cpu_to_read = find_cpu_to_read(event);
>>> +
>>> + if (cpu_to_read >= 0) {
>>> struct perf_read_data data = {
>>> .event = event,
>>> .group = group,
>>> .ret = 0,
>>> };
>>> - ret = smp_call_function_single(event->oncpu,
>>> + ret = smp_call_function_single(cpu_to_read,
>>> __perf_event_read, &data,
>>> 1);
>>> ret = ret ? : data.ret;
>>> } else if (event->state == PERF_EVENT_STATE_INACTIVE) {
>>>
>>
>> I would like to suggest a small change to this patch. I think the check on
>> PERF_EVENT_STATE_ACTIVE should be retained in the perf_event_read()
>> function. The new function should assume that the event is active. I find
>> this more readable since the next check in function perf_event_read() is on
>> PERF_EVENT_STATE_INACTIVE.
>
> Two oncoming flags that Intel CQM/CMT will use are meant to allow read
> even if event is inactive. This makes sense in CQM/CMT because the hw
> RMID is always reserved. I am ok with keeping the check for
> STATE_ACTIVE until those flags are actually introduced, tough.
Hello David
Lets go with checking PERF_EVENT_STATE_ACTIVE in perf_event_read() for
the time being. With the new version of the patch that you posted, I
find that checking PERF_EVENT_STATE_ACTIVE in find_cpu_to_read() makes
you introduce another if statement for checking STATE_INACTIVE.
If your CQM/CMT patches later need the code structure you have now, I
would also support it. But as of now, I think, it is better to check
STATE_ACTIVE in perf_event_read().
Thanks
Nilay
