Commit-ID: 16160c1946b702dcfa95ef63389a56deb2f1c7cb Gitweb: https://git.kernel.org/tip/16160c1946b702dcfa95ef63389a56deb2f1c7cb Author: Jacek Tomaka <jacek.tom...@poczta.fm> AuthorDate: Thu, 2 Aug 2018 09:38:30 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 10 Sep 2018 10:03:01 +0200
perf/x86/intel: Add support/quirk for the MISPREDICT bit on Knights Landing CPUs Problem: perf did not show branch predicted/mispredicted bit in brstack. Output of perf -F brstack for profile collected Before: 0x4fdbcd/0x4fdc03/-/-/-/0 0x45f4c1/0x4fdba0/-/-/-/0 0x45f544/0x45f4bb/-/-/-/0 0x45f555/0x45f53c/-/-/-/0 0x7f66901cc24b/0x45f555/-/-/-/0 0x7f66901cc22e/0x7f66901cc23d/-/-/-/0 0x7f66901cc1ff/0x7f66901cc20f/-/-/-/0 0x7f66901cc1e8/0x7f66901cc1fc/-/-/-/0 After: 0x4fdbcd/0x4fdc03/P/-/-/0 0x45f4c1/0x4fdba0/P/-/-/0 0x45f544/0x45f4bb/P/-/-/0 0x45f555/0x45f53c/P/-/-/0 0x7f66901cc24b/0x45f555/P/-/-/0 0x7f66901cc22e/0x7f66901cc23d/P/-/-/0 0x7f66901cc1ff/0x7f66901cc20f/P/-/-/0 0x7f66901cc1e8/0x7f66901cc1fc/P/-/-/0 Cause: As mentioned in Software Development Manual vol 3, 17.4.8.1, IA32_PERF_CAPABILITIES[5:0] indicates the format of the address that is stored in the LBR stack. Knights Landing reports 1 (LBR_FORMAT_LIP) as its format. Despite that, registers containing FROM address of the branch, do have MISPREDICT bit but because of the format indicated in IA32_PERF_CAPABILITIES[5:0], LBR did not read MISPREDICT bit. Solution: Teach LBR about above Knights Landing quirk and make it read MISPREDICT bit. Signed-off-by: Jacek Tomaka <jacek.tom...@poczta.fm> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/20180802013830.10600-1-jac...@dugeo.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/events/intel/lbr.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c index f3e006bed9a7..c88ed39582a1 100644 --- a/arch/x86/events/intel/lbr.c +++ b/arch/x86/events/intel/lbr.c @@ -1272,4 +1272,8 @@ void intel_pmu_lbr_init_knl(void) x86_pmu.lbr_sel_mask = LBR_SEL_MASK; x86_pmu.lbr_sel_map = snb_lbr_sel_map; + + /* Knights Landing does have MISPREDICT bit */ + if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_LIP) + x86_pmu.intel_cap.lbr_format = LBR_FORMAT_EIP_FLAGS; }
