It's possible to run into issues with re-using unused monitoring IDs
because there may be stale cachelines associated with that ID from a
previous allocation. This can cause the LLC occupancy values to be
inaccurate.

To attempt to mitigate this problem we place the IDs on a least recently
used list, essentially a FIFO. The basic idea is that the longer the
time period between ID re-use the lower the probability that stale
cachelines exist in the cache.
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kanaka Juvva <kanaka.d.juvva@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Link: http://lkml.kernel.org/r/1422038748-21397-7-git-send-email-matt@codeblueprint.co.ukSigned-off-by: NIngo Molnar <mingo@kernel.org>