perf/x86: Add Intel LBR sharing logic
The Intel LBR on some recent processor is capable of filtering branches by type. The filter is configurable via the LBR_SELECT MSR register. There are limitation on how this register can be used. On Nehalem/Westmere, the LBR_SELECT is shared by the two HT threads when HT is on. It is private to each core when HT is off. On SandyBridge, the LBR_SELECT register is private to each thread when HT is on. It is private to each core when HT is off. The kernel must manage the sharing of LBR_SELECT. It allows multiple users on the same logical CPU to use LBR_SELECT as long as they program it with the same value. Across sibling CPUs (HT threads), the same restriction applies on NHM/WSM. This patch implements this sharing logic by leveraging the mechanism put in place for managing the offcore_response shared MSR. We modify __intel_shared_reg_get_constraints() to cause x86_get_event_constraint() to be called because LBR may be associated with events that may be counter constrained. Signed-off-by: Stephane Eranian <eranian@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1328826068-11713-4-git-send-email-eranian@google.comSigned-off-by: Ingo Molnar <mingo@elte.hu>
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