Re: [PATCH 4/7] perf/x86-ibs: Add support for IBS pseudo events

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2012-05-02 at 20:26 +0200, Robert Richter wrote:
> +enum ibs_filter_type {
> +       IBS_NO_FILTER           = 0,
> +       IBS_MATCH_FILTER        = 1,
> +       IBS_ANY_SET_FILTER      = 2,
> +       IBS_PSEUDO_EVENT        = 0x0F,
> +};

I don't get how those pseudo events work, AFAIKT IBS_PSEUDO_EVENT causes
one to loose all events since it does have a filter set but fails the
filter and thus we skip the call to perf_event_overflow().

Furthermore, I think this filter stuff should accumulate the period so
that PERF_SAMPLE_PERIOD still works correctly and reflects the number of
counts since the last sample.

Also, what's the point of filtering in-kernel as opposed to doing all
this in userspace? Is the amount of data 'saved' significant enough?