path: root/arch/powerpc/perf
diff options
authorAnton Blanchard <anton@samba.org>2012-06-26 01:02:15 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2012-07-10 19:18:43 +1000
commit5c093efa6f2dd07d45835be870a20ed3b05b6ef5 (patch)
tree3f089f5c5c4c2a6bc2633df1e3b4f28289361402 /arch/powerpc/perf
parent75382aa72f06823db7312ad069c3bae2eb3f8548 (diff)
powerpc/perf: Always use pt_regs for userspace samples
At the moment we always use the SIAR if the PMU supports continuous sampling. Unfortunately the SIAR and the PMU exception are not synchronised for non marked events so we can end up with callchains that dont make sense. The following patch checks the HV and PR bits for samples coming from userspace and always uses pt_regs for them. Userspace will never have interrupts off so there is no real advantage to using the SIAR for non marked events in userspace. I had experimented with a patch that did a similar thing for kernel samples but we lost a significant amount of information. I was unable to profile any of our early exception code for example. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/perf')
1 files changed, 22 insertions, 1 deletions
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index dcb6a798f11..77b49ddda9d 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -189,9 +189,30 @@ static inline void perf_read_regs(struct pt_regs *regs)
int marked = mmcra & MMCRA_SAMPLE_ENABLE;
int use_siar;
+ /*
+ * If this isn't a PMU exception (eg a software event) the SIAR is
+ * not valid. Use pt_regs.
+ *
+ * If it is a marked event use the SIAR.
+ *
+ * If the PMU doesn't update the SIAR for non marked events use
+ * pt_regs.
+ *
+ * If the PMU has HV/PR flags then check to see if they
+ * place the exception in userspace. If so, use pt_regs. In
+ * continuous sampling mode the SIAR and the PMU exception are
+ * not synchronised, so they may be many instructions apart.
+ * This can result in confusing backtraces. We still want
+ * hypervisor samples as well as samples in the kernel with
+ * interrupts off hence the userspace check.
+ */
if (TRAP(regs) != 0xf00)
use_siar = 0;
- else if ((ppmu->flags & PPMU_NO_CONT_SAMPLING) && !marked)
+ else if (marked)
+ use_siar = 1;
+ else if ((ppmu->flags & PPMU_NO_CONT_SAMPLING))
+ use_siar = 0;
+ else if (!(ppmu->flags & PPMU_NO_SIPR) && mmcra_sipr(mmcra))
use_siar = 0;
use_siar = 1;