powerpc/oprofile: Handle events that raise an exception without overflowing

[linux-flexiantxendom0-natty.git] / arch / powerpc / oprofile / op_model_power4.c

diff --git a/arch/powerpc/oprofile/op_model_power4.c b/arch/powerpc/oprofile/op_model_power4.c
index 8077409..93636ca 100644 (file)
--- a/arch/powerpc/oprofile/op_model_power4.c
+++ b/arch/powerpc/oprofile/op_model_power4.c
@@ -261,6 +261,28 @@ static int get_kernel(unsigned long pc, unsigned long mmcra)
        return is_kernel;
 }
 
+static bool pmc_overflow(unsigned long val)
+{
+       if ((int)val < 0)
+               return true;
+
+       /*
+        * Events on POWER7 can roll back if a speculative event doesn't
+        * eventually complete. Unfortunately in some rare cases they will
+        * raise a performance monitor exception. We need to catch this to
+        * ensure we reset the PMC. In all cases the PMC will be 256 or less
+        * cycles from overflow.
+        *
+        * We only do this if the first pass fails to find any overflowing
+        * PMCs because a user might set a period of less than 256 and we
+        * don't want to mistakenly reset them.
+        */
+       if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))
+               return true;
+
+       return false;
+}
+
 static void power4_handle_interrupt(struct pt_regs *regs,
                                    struct op_counter_config *ctr)
 {
@@ -281,7 +303,7 @@ static void power4_handle_interrupt(struct pt_regs *regs,
 
        for (i = 0; i < cur_cpu_spec->num_pmcs; ++i) {
                val = classic_ctr_read(i);
-               if (val < 0) {
+               if (pmc_overflow(val)) {
                        if (oprofile_running && ctr[i].enabled) {
                                oprofile_add_ext_sample(pc, regs, i, is_kernel);
                                classic_ctr_write(i, reset_value[i]);