summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/cpu/perf_event.c
diff options
context:
space:
mode:
authorAndi Kleen <ak@linux.intel.com>2015-02-17 18:18:06 -0800
committerIngo Molnar <mingo@kernel.org>2015-03-27 09:14:03 +0100
commit294fe0f52a44c6f207211de0686c369a961b5533 (patch)
tree0802f465bd807ee3b0e9e6ecc4522033beb92522 /arch/x86/kernel/cpu/perf_event.c
parent91f1b70582c62576f429cf78d53751c66677553d (diff)
perf/x86/intel: Add INST_RETIRED.ALL workarounds
On Broadwell INST_RETIRED.ALL cannot be used with any period that doesn't have the lowest 6 bits cleared. And the period should not be smaller than 128. This is erratum BDM11 and BDM55: http://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/5th-gen-core-family-spec-update.pdf BDM11: When using a period < 100; we may get incorrect PEBS/PMI interrupts and/or an invalid counter state. BDM55: When bit0-5 of the period are !0 we may get redundant PEBS records on overflow. Add a new callback to enforce this, and set it for Broadwell. How does this handle the case when an app requests a specific period with some of the bottom bits set? Short answer: Any useful instruction sampling period needs to be 4-6 orders of magnitude larger than 128, as an PMI every 128 instructions would instantly overwhelm the system and be throttled. So the +-64 error from this is really small compared to the period, much smaller than normal system jitter. Long answer (by Peterz): IFF we guarantee perf_event_attr::sample_period >= 128. Suppose we start out with sample_period=192; then we'll set period_left to 192, we'll end up with left = 128 (we truncate the lower bits). We get an interrupt, find that period_left = 64 (>0 so we return 0 and don't get an overflow handler), up that to 128. Then we trigger again, at n=256. Then we find period_left = -64 (<=0 so we return 1 and do get an overflow). We increment with sample_period so we get left = 128. We fire again, at n=384, period_left = 0 (<=0 so we return 1 and get an overflow). And on and on. So while the individual interrupts are 'wrong' we get then with interval=256,128 in exactly the right ratio to average out at 192. And this works for everything >=128. So the num_samples*fixed_period thing is still entirely correct +- 127, which is good enough I'd say, as you already have that error anyhow. So no need to 'fix' the tools, al we need to do is refuse to create INST_RETIRED:ALL events with sample_period < 128. Signed-off-by: Andi Kleen <ak@linux.intel.com> [ Updated comments and changelog a bit. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: http://lkml.kernel.org/r/1424225886-18652-3-git-send-email-andi@firstfloor.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/cpu/perf_event.c')
-rw-r--r--arch/x86/kernel/cpu/perf_event.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index e0dab5ce61e9..ec6e982fd464 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -451,6 +451,12 @@ int x86_pmu_hw_config(struct perf_event *event)
if (event->attr.type == PERF_TYPE_RAW)
event->hw.config |= event->attr.config & X86_RAW_EVENT_MASK;
+ if (event->attr.sample_period && x86_pmu.limit_period) {
+ if (x86_pmu.limit_period(event, event->attr.sample_period) >
+ event->attr.sample_period)
+ return -EINVAL;
+ }
+
return x86_setup_perfctr(event);
}
@@ -988,6 +994,9 @@ int x86_perf_event_set_period(struct perf_event *event)
if (left > x86_pmu.max_period)
left = x86_pmu.max_period;
+ if (x86_pmu.limit_period)
+ left = x86_pmu.limit_period(event, left);
+
per_cpu(pmc_prev_left[idx], smp_processor_id()) = left;
/*