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With LBRv5 reading the extra LBR flags like mispredict, TSX, cycles is not free anymore, as it has moved to a separate MSR. For callstack mode we don't need any of this information; so we can avoid the unnecessary MSR read. Add flags to the perf interface where perf record can request not collecting this information. Add branch_sample_type flags for CYCLES and FLAGS. It's a bit unusual for branch_sample_types to be negative (disable), not positive (enable), but since the legacy ABI reported the flags we need some form of explicit disabling to avoid breaking the ABI. After we have the flags the x86 perf code can keep track if any users need the flags. If noone needs it the information is not collected. This cuts down the cost of LBR callstack on Skylake significantly. Profiling a kernel build with LBR call stack the average run time of the PMI handler drops by 43%. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Cc: acme@kernel.org Cc: jolsa@kernel.org Link: http://lkml.kernel.org/r/1445366797-30894-2-git-send-email-andi@firstfloor.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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