[PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

Stephane Eranian
2012-06-07T07:15:43Z

This patch checks the microcode version before disabling
PEBS on SandyBridge model 42 (desktop, mobile), and 45 (SNB-EP).
PEBS was disabled for both models due to an erratum.

A workaround is implemented by micro-code 0x28. This patch checks
the microcode version and disables PEBS support if version < 0x28.
The check is done each time a PEBS event is created and NOT at boot
time because the micro-code update may only be done after the kernel
has booted.

Go to downloadcenter.intel.com to download microcode updates.
Need microcode update 6/6/2012 or later.

Signed-off-by: Stephane Eranian <eranian@google.com>

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 5ec146c..9c905bd 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1394,6 +1394,27 @@ static void intel_pebs_aliases_snb(struct perf_event *event)
}
}

+static int check_pebs_quirks(void)
+{
+ int uversion = cpu_data(smp_processor_id()).microcode;
+ int model = cpu_data(smp_processor_id()).x86_model;
+
+ /* do not have PEBS to begin with */
+ if (!x86_pmu.pebs)
+ return 0;
+
+ /*
+ * check ucode version for SNB, SNB-EP
+ */
+ if ((model == 42 || model == 45) && uversion < 0x28) {
+ pr_warn("SandyBridge PEBS unavailable due to CPU erratum, "
+ " update microcode (was 0x%x, needs at least 0x28).\n",
+ uversion);
+ return -ENOTSUPP;
+ }
+ return 0;
+}
+
static int intel_pmu_hw_config(struct perf_event *event)
{
int ret = x86_pmu_hw_config(event);
@@ -1401,8 +1422,14 @@ static int intel_pmu_hw_config(struct perf_event *event)
if (ret)
return ret;

- if (event->attr.precise_ip && x86_pmu.pebs_aliases)
- x86_pmu.pebs_aliases(event);
+ if (event->attr.precise_ip) {
+
+ if (check_pebs_quirks())
+ return -ENOTSUPP;
+
+ if (x86_pmu.pebs_aliases)
+ x86_pmu.pebs_aliases(event);
+ }

if (intel_pmu_needs_lbr_smpl(event)) {
ret = intel_pmu_setup_lbr_filter(event);
@@ -1714,13 +1741,6 @@ static __init void intel_clovertown_quirk(void)
x86_pmu.pebs_constraints = NULL;
}

-static __init void intel_sandybridge_quirk(void)
-{
- pr_warn("PEBS disabled due to CPU errata\n");
- x86_pmu.pebs = 0;
- x86_pmu.pebs_constraints = NULL;
-}
-
static const struct { int id; char *name; } intel_arch_events_map[] __initconst = {
{ PERF_COUNT_HW_CPU_CYCLES, "cpu cycles" },
{ PERF_COUNT_HW_INSTRUCTIONS, "instructions" },
@@ -1914,7 +1934,6 @@ __init int intel_pmu_init(void)

case 42: /* SandyBridge */
case 45: /* SandyBridge, "Romely-EP" */
- x86_add_quirk(intel_sandybridge_quirk);
case 58: /* IvyBridge */
memcpy(hw_cache_event_ids, snb_hw_cache_event_ids,
sizeof(hw_cache_event_ids));