Quoting Lionel Landwerlin (2019-01-16 17:36:22)

With the currently available parameters for the i915-perf stream,
there are still situations that are not well covered :

If an application opens the stream with polling disable or at very low
frequency and OA interrupt enabled, no data will be available even
though somewhere between nothing and half of the OA buffer worth of
data might have landed in memory.

To solve this issue we have a new flush ioctl on the perf stream that
forces the i915-perf driver to look at the state of the buffer when
called and makes any data available through both poll() & read() type
syscalls.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

Link to userspace changes?

Regards, Joonas