Re: [RFC PATCH 2/2] perf stat: Use event group to simulate PMI onPMI-less hardware counter

[Peter Zijlstra]

On Wed, 2010-11-10 at 14:15 +0800, Lin Ming wrote:
> Some hardware counters(for example, Intel RAPL) can't generate interrupt
> when overflow. So we need to simulate the interrupt to periodically
> record the counter values. Otherwise, the counter may overflow and the
> wrong value is read.
> 
> This patch uses event group to simulate PMI as suggested by Peter
> Zijlstra, http://marc.info/?l=linux-kernel&m=128220854801819&w=2
> 
> create_group_counters() will create a group with 2 events, one hrtimer
> based event as the group leader, and the other event to count. The
> hrtimer is fired periodically, so the sibling event can record its
> counter value periodically as well.

I'm terribly confused here....

 - you introduce perf_event_attr:pmi_simulate, but then you never
implement it -- nor do we need it afaict.


 - you use grouped counters for perf-stat, perf-stat doesn't use
sampling so I don't see a need to group events to simulate the PMI.


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