commit 5f5092e7 upstream.

Since we indirect all of our PMU IRQ handling through a dispatcher, it's
trivial to hook up perf_sample_event_took to prevent applications such
as oprofile from generating interrupt storms due to an unrealisticly
low sample period.
Reported-by: Robert Richter <rric@kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>