On Mon, Jul 30, 2018 at 10:28:13PM +0800, Jacek Tomaka wrote: > From: Jacek Tomaka <[email protected]> > > 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. > --- > arch/x86/events/intel/lbr.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c > index cf372b9055..043aa09f3a 100644 > --- a/arch/x86/events/intel/lbr.c > +++ b/arch/x86/events/intel/lbr.c > @@ -19,7 +19,7 @@ enum { > LBR_FORMAT_MAX_KNOWN = LBR_FORMAT_TIME, > }; > > -static const enum { > +static enum { > LBR_EIP_FLAGS = 1, > LBR_TSX = 2, > } lbr_desc[LBR_FORMAT_MAX_KNOWN + 1] = { > @@ -1230,4 +1230,8 @@ 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) > + lbr_desc[LBR_FORMAT_LIP] |= LBR_EIP_FLAGS; > }
So why not set lbr_format to LBR_FORMAT_EIP_FLAGS ?
