linux-kernel - [tip:perfcounters/core] perf_counter: x86: Fix throttling

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Date:	Fri, 15 May 2009 08:42:42 GMT
From:	tip-bot for Ingo Molnar <mingo@...e.hu>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	cjashfor@...ux.vnet.ibm.com, mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter: x86: Fix throttling

Commit-ID:  f5a5a2f6e69e88647ae12da39f0ff3a510bcf0a6
Gitweb:     http://git.kernel.org/tip/f5a5a2f6e69e88647ae12da39f0ff3a510bcf0a6
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Wed, 13 May 2009 12:54:01 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 15 May 2009 09:46:56 +0200

perf_counter: x86: Fix throttling

If counters are disabled globally when a perfcounter IRQ/NMI hits,
and if we throttle in that case, we'll promote the '0' value to
the next lapic IRQ and disable all perfcounters at that point,
permanently ...

Fix it.

[ Impact: fix hung perfcounters under load ]

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 arch/x86/kernel/cpu/perf_counter.c |   20 +++++++++++++++-----
 1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index 3a92a2b..88ae8ce 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -765,8 +765,13 @@ out:
 	/*
 	 * Restore - do not reenable when global enable is off or throttled:
 	 */
-	if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS)
-		intel_pmu_restore_all(cpuc->throttle_ctrl);
+	if (cpuc->throttle_ctrl) {
+		if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS) {
+			intel_pmu_restore_all(cpuc->throttle_ctrl);
+		} else {
+			pr_info("CPU#%d: perfcounters: max interrupt rate exceeded! Throttle on.\n", smp_processor_id());
+		}
+	}
 
 	return ret;
 }
@@ -817,11 +822,16 @@ void perf_counter_unthrottle(void)
 
 	cpuc = &__get_cpu_var(cpu_hw_counters);
 	if (cpuc->interrupts >= PERFMON_MAX_INTERRUPTS) {
-		if (printk_ratelimit())
-			printk(KERN_WARNING "perfcounters: max interrupts exceeded!\n");
+		pr_info("CPU#%d: perfcounters: throttle off.\n", smp_processor_id());
+
+		/*
+		 * Clear them before re-enabling irqs/NMIs again:
+		 */
+		cpuc->interrupts = 0;
 		hw_perf_restore(cpuc->throttle_ctrl);
+	} else {
+		cpuc->interrupts = 0;
 	}
-	cpuc->interrupts = 0;
 }
 
 void smp_perf_counter_interrupt(struct pt_regs *regs)
--
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