From 506e70d13236dfdb0bc15e0914298ab0a7b7f4df Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Mon, 13 May 2013 18:44:57 +0000 Subject: powerpc/pmu: Fix order of interpreting BHRB target entries The current Branch History Rolling Buffer (BHRB) code misinterprets the order of entries in the hardware buffer. It assumes that a branch target address will be read _after_ its corresponding branch. In reality the branch target comes before (lower mfbhrb entry) it's corresponding branch. This is a rewrite of the code to take this into account. Signed-off-by: Michael Neuling Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/perf/core-book3s.c | 89 +++++++++++++++++++++-------------------- 1 file changed, 46 insertions(+), 43 deletions(-) (limited to 'arch/powerpc/perf') diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 843bb8be838..3fdfe4575b8 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -363,72 +363,75 @@ void power_pmu_flush_branch_stack(void) power_pmu_bhrb_reset(); } - /* Processing BHRB entries */ -static void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw) +void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw) { u64 val; u64 addr; - int r_index, u_index, target, pred; + int r_index, u_index, pred; r_index = 0; u_index = 0; while (r_index < ppmu->bhrb_nr) { /* Assembly read function */ - val = read_bhrb(r_index); - - /* Terminal marker: End of valid BHRB entries */ - if (val == 0) { + val = read_bhrb(r_index++); + if (!val) + /* Terminal marker: End of valid BHRB entries */ break; - } else { - /* BHRB field break up */ + else { addr = val & BHRB_EA; pred = val & BHRB_PREDICTION; - target = val & BHRB_TARGET; - /* Probable Missed entry: Not applicable for POWER8 */ - if ((addr == 0) && (target == 0) && (pred == 1)) { - r_index++; + if (!addr) + /* invalid entry */ continue; - } - /* Real Missed entry: Power8 based missed entry */ - if ((addr == 0) && (target == 1) && (pred == 1)) { - r_index++; - continue; - } - - /* Reserved condition: Not a valid entry */ - if ((addr == 0) && (target == 1) && (pred == 0)) { - r_index++; - continue; - } + /* Branches are read most recent first (ie. mfbhrb 0 is + * the most recent branch). + * There are two types of valid entries: + * 1) a target entry which is the to address of a + * computed goto like a blr,bctr,btar. The next + * entry read from the bhrb will be branch + * corresponding to this target (ie. the actual + * blr/bctr/btar instruction). + * 2) a from address which is an actual branch. If a + * target entry proceeds this, then this is the + * matching branch for that target. If this is not + * following a target entry, then this is a branch + * where the target is given as an immediate field + * in the instruction (ie. an i or b form branch). + * In this case we need to read the instruction from + * memory to determine the target/to address. + */ - /* Is a target address */ if (val & BHRB_TARGET) { - /* First address cannot be a target address */ - if (r_index == 0) { - r_index++; - continue; - } - - /* Update target address for the previous entry */ - cpuhw->bhrb_entries[u_index - 1].to = addr; - cpuhw->bhrb_entries[u_index - 1].mispred = pred; - cpuhw->bhrb_entries[u_index - 1].predicted = ~pred; + /* Target branches use two entries + * (ie. computed gotos/XL form) + */ + cpuhw->bhrb_entries[u_index].to = addr; + cpuhw->bhrb_entries[u_index].mispred = pred; + cpuhw->bhrb_entries[u_index].predicted = ~pred; - /* Dont increment u_index */ - r_index++; + /* Get from address in next entry */ + val = read_bhrb(r_index++); + addr = val & BHRB_EA; + if (val & BHRB_TARGET) { + /* Shouldn't have two targets in a + row.. Reset index and try again */ + r_index--; + addr = 0; + } + cpuhw->bhrb_entries[u_index].from = addr; } else { - /* Update address, flags for current entry */ + /* Branches to immediate field + (ie I or B form) */ cpuhw->bhrb_entries[u_index].from = addr; + cpuhw->bhrb_entries[u_index].to = 0; cpuhw->bhrb_entries[u_index].mispred = pred; cpuhw->bhrb_entries[u_index].predicted = ~pred; - - /* Successfully popullated one entry */ - u_index++; - r_index++; } + u_index++; + } } cpuhw->bhrb_stack.nr = u_index; -- cgit v1.2.3