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 <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 843bb8b..3fdfe45 100644 (file)
--- 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;