[PATCH 17/31] perf, x86: Avoid checkpointed counters causing excessive TSX aborts

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

With checkpointed counters there can be a situation where the counter
is overflowing, aborts the transaction, is set back to a non overflowing
checkpoint, causes interupt. The interrupt doesn't see the overflow
because it has been checkpointed.  This is then a spurious PMI, typically with a
ugly NMI message.  It can also lead to excessive aborts.

Avoid this problem by:
- Using the full counter width for counting counters (previous patch)
- Forbid sampling for checkpointed counters. It's not too useful anyways,
checkpointing is mainly for counting.
- On a PMI always set back checkpointed counters to zero.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/kernel/cpu/perf_event_intel.c |   26 +++++++++++++++++++++++++-
 1 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index e302186..83ced1a 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1079,6 +1079,17 @@ static void intel_pmu_enable_event(struct perf_event *event)
 int intel_pmu_save_and_restart(struct perf_event *event)
 {
 	x86_perf_event_update(event);
+	/*
+	 * For a checkpointed counter always reset back to 0.  This
+	 * avoids a situation where the counter overflows, aborts the
+	 * transaction and is then set back to shortly before the
+	 * overflow, and overflows and aborts again.
+	 */
+	if (event->attr.intx_checkpointed) {
+		/* No race with NMIs because the counter should not be armed */
+		wrmsrl(event->hw.event_base, 0);
+		local64_set(&event->hw.prev_count, 0);
+	}
 	return x86_perf_event_set_period(event);
 }
 
@@ -1162,6 +1173,10 @@ again:
 		x86_pmu.drain_pebs(regs);
 	}
 
+	/* XXX move somewhere else. */
+	if (cpuc->events[2] && cpuc->events[2]->attr.intx_checkpointed)
+		status |= (1ULL << 2);
+
 	for_each_set_bit(bit, (unsigned long *)&status, X86_PMC_IDX_MAX) {
 		struct perf_event *event = cpuc->events[bit];
 
@@ -1626,8 +1641,17 @@ static int hsw_hw_config(struct perf_event *event)
 		return 0;
 	if (event->attr.intx)
 		event->hw.config |= HSW_INTX;
-	if (event->attr.intx_checkpointed)
+	if (event->attr.intx_checkpointed) {
+		/*
+		 * Sampling of checkpointed events can cause situations where
+		 * the CPU constantly aborts because of a overflow, which is
+		 * then checkpointed back and ignored. Forbid checkpointing
+		 * for sampling.
+		 */
+		if (is_sampling_event(event))
+			return -EIO;
 		event->hw.config |= HSW_INTX_CHECKPOINTED;
+	}
 	return 0;
 }
 
-- 
1.7.7.6