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 <mi...@neuling.org>
---
arch/powerpc/perf/core-book3s.c | 86 ++++++++++++++++++++-------------------
1 file changed, 45 insertions(+), 41 deletions(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index c627843..2d81372 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1463,66 +1463,70 @@ 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;
--
1.7.10.4
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