From: Jacek Tomaka jacek.tomaka@poczta.fm
[ Upstream commit 16160c1946b702dcfa95ef63389a56deb2f1c7cb ]
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.tomaka@poczta.fm Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/20180802013830.10600-1-jacekt@dugeo.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- 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 5d103a87e984..be0ad713ad5e 100644 --- a/arch/x86/events/intel/lbr.c +++ b/arch/x86/events/intel/lbr.c @@ -1175,4 +1175,8 @@ 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; }