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Date: Fri, 23 Jan 2009 14:07:10 +0100
From: Mike Galbraith <efault@....de>
To: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
LKML <linux-kernel@...r.kernel.org>
Subject: [patch] ratelimit performance counter interrupts
While fiddling around with kerneltop, I found that an unwary user can
lock his box up quite thoroughly if he does something really clever like
starting kerneltop with -c 100.
Ratelimit performance counter interrupts to 100KHz per CPU.
Signed-off-by: Mike Galbraith <efault@....de>
---
arch/x86/kernel/apic.c | 2 +
arch/x86/kernel/cpu/perf_counter.c | 43 ++++++++++++++++++++++++++++++-------
include/linux/perf_counter.h | 2 +
3 files changed, 40 insertions(+), 7 deletions(-)
Index: linux-2.6/arch/x86/kernel/apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic.c
+++ linux-2.6/arch/x86/kernel/apic.c
@@ -781,6 +781,8 @@ static void local_apic_timer_interrupt(v
inc_irq_stat(apic_timer_irqs);
evt->event_handler(evt);
+
+ perf_counter_unthrottle();
}
/*
Index: linux-2.6/arch/x86/kernel/cpu/perf_counter.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_counter.c
+++ linux-2.6/arch/x86/kernel/cpu/perf_counter.c
@@ -33,6 +33,8 @@ static int nr_counters_fixed __read_most
struct cpu_hw_counters {
struct perf_counter *counters[X86_PMC_IDX_MAX];
unsigned long used[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
+ unsigned long interrupts;
+ u64 global_enable;
};
/*
@@ -468,23 +470,26 @@ perf_handle_group(struct perf_counter *s
}
/*
+ * Mamimum interrupt frequency of 100KHz per CPU
+ */
+#define PERFMON_MAX_INTERRUPTS 100000/HZ
+
+/*
* This handler is triggered by the local APIC, so the APIC IRQ handling
* rules apply:
*/
static void __smp_perf_counter_interrupt(struct pt_regs *regs, int nmi)
{
int bit, cpu = smp_processor_id();
- u64 ack, status, saved_global;
- struct cpu_hw_counters *cpuc;
+ u64 ack, status;
+ struct cpu_hw_counters *cpuc = &per_cpu(cpu_hw_counters, cpu);
- rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, saved_global);
+ rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);
/* Disable counters globally */
wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0);
ack_APIC_irq();
- cpuc = &per_cpu(cpu_hw_counters, cpu);
-
rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, status);
if (!status)
goto out;
@@ -533,9 +538,33 @@ again:
goto again;
out:
/*
- * Restore - do not reenable when global enable is off:
+ * Restore - do not reenable when global enable is off or throttled:
*/
- wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, saved_global);
+ if (++cpuc->interrupts < PERFMON_MAX_INTERRUPTS)
+ wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);
+}
+
+void perf_counter_unthrottle(void)
+{
+ struct cpu_hw_counters *cpuc;
+ u64 global_enable;
+
+ if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON))
+ return;
+
+ if (unlikely(!perf_counters_initialized))
+ return;
+
+ cpuc = &per_cpu(cpu_hw_counters, smp_processor_id());
+ if (cpuc->interrupts >= PERFMON_MAX_INTERRUPTS) {
+ if (printk_ratelimit())
+ printk(KERN_WARNING "PERFMON: max interrupts exceeded!\n");
+ wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);
+ }
+ rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, global_enable);
+ if (unlikely(cpuc->global_enable && !global_enable))
+ wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, cpuc->global_enable);
+ cpuc->interrupts = 0;
}
void smp_perf_counter_interrupt(struct pt_regs *regs)
Index: linux-2.6/include/linux/perf_counter.h
===================================================================
--- linux-2.6.orig/include/linux/perf_counter.h
+++ linux-2.6/include/linux/perf_counter.h
@@ -254,6 +254,7 @@ extern void perf_counter_init_task(struc
extern void perf_counter_exit_task(struct task_struct *child);
extern void perf_counter_notify(struct pt_regs *regs);
extern void perf_counter_print_debug(void);
+extern void perf_counter_unthrottle(void);
extern u64 hw_perf_save_disable(void);
extern void hw_perf_restore(u64 ctrl);
extern int perf_counter_task_disable(void);
@@ -281,6 +282,7 @@ static inline void perf_counter_init_tas
static inline void perf_counter_exit_task(struct task_struct *child) { }
static inline void perf_counter_notify(struct pt_regs *regs) { }
static inline void perf_counter_print_debug(void) { }
+static inline void perf_counter_unthrottle(void) { }
static inline void hw_perf_restore(u64 ctrl) { }
static inline u64 hw_perf_save_disable(void) { return 0; }
static inline int perf_counter_task_disable(void) { return -EINVAL; }
--
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