linux-kernel - Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters

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Date:	Thu, 16 Sep 2010 19:34:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <robert.richter@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, Don Zickus <dzickus@...hat.com>,
	"gorcunov@...il.com" <gorcunov@...il.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ying.huang@...el.com" <ying.huang@...el.com>,
	"ming.m.lin@...el.com" <ming.m.lin@...el.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"eranian@...gle.com" <eranian@...gle.com>
Subject: Re: [PATCH] perf, x86: catch spurious interrupts after disabling
 counters

On Wed, 2010-09-15 at 18:20 +0200, Robert Richter wrote:
> Some cpus still deliver spurious interrupts after disabling a counter.
> This caused 'undelivered NMI' messages. This patch fixes this.
> 
I tried the below and that also seems to work.. So yeah, looks like
we're getting late NMIs.

---
 arch/x86/kernel/cpu/perf_event.c |   21 ++++++++++++++++++++-
 1 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 0fb1705..9a261ac 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1145,6 +1145,22 @@ static void x86_pmu_del(struct perf_event *event, int flags)
 	perf_event_update_userpage(event);
 }
 
+static int fixup_overflow(int idx)
+{
+	u64 val;
+
+	rdmsrl(x86_pmu.perfctr + idx, val);
+	if (!(val & (1ULL << (x86_pmu.cntval_bits - 1)))) {
+		val = (u64)(-x86_pmu.max_period);
+		val &= x86_pmu.cntval_mask;
+		wrmsrl(x86_pmu.perfctr + idx, val);
+
+		return 1;
+	}
+
+	return 0;
+}
+
 static int x86_pmu_handle_irq(struct pt_regs *regs)
 {
 	struct perf_sample_data data;
@@ -1159,8 +1175,11 @@ static int x86_pmu_handle_irq(struct pt_regs *regs)
 	cpuc = &__get_cpu_var(cpu_hw_events);
 
 	for (idx = 0; idx < x86_pmu.num_counters; idx++) {
-		if (!test_bit(idx, cpuc->active_mask))
+		if (!test_bit(idx, cpuc->active_mask)) {
+	       		if (fixup_overflow(idx))
+				handled++;
 			continue;
+		}
 
 		event = cpuc->events[idx];
 		hwc = &event->hw;

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