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-rw-r--r--Documentation/sysctl/kernel.txt26
-rw-r--r--arch/x86/kernel/cpu/perf_event.c12
-rw-r--r--include/linux/perf_event.h7
-rw-r--r--kernel/events/core.c92
-rw-r--r--kernel/sysctl.c9
5 files changed, 141 insertions, 5 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 9b34b168507..8d90c42e5db 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -438,6 +438,32 @@ This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
==============================================================
+perf_cpu_time_max_percent:
+
+Hints to the kernel how much CPU time it should be allowed to
+use to handle perf sampling events. If the perf subsystem
+is informed that its samples are exceeding this limit, it
+will drop its sampling frequency to attempt to reduce its CPU
+usage.
+
+Some perf sampling happens in NMIs. If these samples
+unexpectedly take too long to execute, the NMIs can become
+stacked up next to each other so much that nothing else is
+allowed to execute.
+
+0: disable the mechanism. Do not monitor or correct perf's
+ sampling rate no matter how CPU time it takes.
+
+1-100: attempt to throttle perf's sample rate to this
+ percentage of CPU. Note: the kernel calculates an
+ "expected" length of each sample event. 100 here means
+ 100% of that expected length. Even if this is set to
+ 100, you may still see sample throttling if this
+ length is exceeded. Set to 0 if you truly do not care
+ how much CPU is consumed.
+
+==============================================================
+
pid_max:
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index a69b67d968d..123d9e2271d 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1252,10 +1252,20 @@ void perf_events_lapic_init(void)
static int __kprobes
perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
{
+ int ret;
+ u64 start_clock;
+ u64 finish_clock;
+
if (!atomic_read(&active_events))
return NMI_DONE;
- return x86_pmu.handle_irq(regs);
+ start_clock = local_clock();
+ ret = x86_pmu.handle_irq(regs);
+ finish_clock = local_clock();
+
+ perf_sample_event_took(finish_clock - start_clock);
+
+ return ret;
}
struct event_constraint emptyconstraint;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c5b6dbf9c2f..229a757e1c1 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -695,10 +695,17 @@ static inline void perf_callchain_store(struct perf_callchain_entry *entry, u64
extern int sysctl_perf_event_paranoid;
extern int sysctl_perf_event_mlock;
extern int sysctl_perf_event_sample_rate;
+extern int sysctl_perf_cpu_time_max_percent;
+
+extern void perf_sample_event_took(u64 sample_len_ns);
extern int perf_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);
+extern int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
+
static inline bool perf_paranoid_tracepoint_raw(void)
{
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0601825adc2..c0f6d9b7d78 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -165,10 +165,26 @@ int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free'
/*
* max perf event sample rate
*/
-#define DEFAULT_MAX_SAMPLE_RATE 100000
-int sysctl_perf_event_sample_rate __read_mostly = DEFAULT_MAX_SAMPLE_RATE;
-static int max_samples_per_tick __read_mostly =
- DIV_ROUND_UP(DEFAULT_MAX_SAMPLE_RATE, HZ);
+#define DEFAULT_MAX_SAMPLE_RATE 100000
+#define DEFAULT_SAMPLE_PERIOD_NS (NSEC_PER_SEC / DEFAULT_MAX_SAMPLE_RATE)
+#define DEFAULT_CPU_TIME_MAX_PERCENT 25
+
+int sysctl_perf_event_sample_rate __read_mostly = DEFAULT_MAX_SAMPLE_RATE;
+
+static int max_samples_per_tick __read_mostly = DIV_ROUND_UP(DEFAULT_MAX_SAMPLE_RATE, HZ);
+static int perf_sample_period_ns __read_mostly = DEFAULT_SAMPLE_PERIOD_NS;
+
+static atomic_t perf_sample_allowed_ns __read_mostly =
+ ATOMIC_INIT( DEFAULT_SAMPLE_PERIOD_NS * DEFAULT_CPU_TIME_MAX_PERCENT / 100);
+
+void update_perf_cpu_limits(void)
+{
+ u64 tmp = perf_sample_period_ns;
+
+ tmp *= sysctl_perf_cpu_time_max_percent;
+ tmp = do_div(tmp, 100);
+ atomic_set(&perf_sample_allowed_ns, tmp);
+}
int perf_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
@@ -180,10 +196,78 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
return ret;
max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
+ perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
+ update_perf_cpu_limits();
return 0;
}
+int sysctl_perf_cpu_time_max_percent __read_mostly = DEFAULT_CPU_TIME_MAX_PERCENT;
+
+int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+ if (ret || !write)
+ return ret;
+
+ update_perf_cpu_limits();
+
+ return 0;
+}
+
+/*
+ * perf samples are done in some very critical code paths (NMIs).
+ * If they take too much CPU time, the system can lock up and not
+ * get any real work done. This will drop the sample rate when
+ * we detect that events are taking too long.
+ */
+#define NR_ACCUMULATED_SAMPLES 128
+DEFINE_PER_CPU(u64, running_sample_length);
+
+void perf_sample_event_took(u64 sample_len_ns)
+{
+ u64 avg_local_sample_len;
+ u64 local_samples_len = __get_cpu_var(running_sample_length);
+
+ if (atomic_read(&perf_sample_allowed_ns) == 0)
+ return;
+
+ /* decay the counter by 1 average sample */
+ local_samples_len = __get_cpu_var(running_sample_length);
+ local_samples_len -= local_samples_len/NR_ACCUMULATED_SAMPLES;
+ local_samples_len += sample_len_ns;
+ __get_cpu_var(running_sample_length) = local_samples_len;
+
+ /*
+ * note: this will be biased artifically low until we have
+ * seen NR_ACCUMULATED_SAMPLES. Doing it this way keeps us
+ * from having to maintain a count.
+ */
+ avg_local_sample_len = local_samples_len/NR_ACCUMULATED_SAMPLES;
+
+ if (avg_local_sample_len <= atomic_read(&perf_sample_allowed_ns))
+ return;
+
+ if (max_samples_per_tick <= 1)
+ return;
+
+ max_samples_per_tick = DIV_ROUND_UP(max_samples_per_tick, 2);
+ sysctl_perf_event_sample_rate = max_samples_per_tick * HZ;
+ perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
+
+ printk_ratelimited(KERN_WARNING
+ "perf samples too long (%lld > %d), lowering "
+ "kernel.perf_event_max_sample_rate to %d\n",
+ avg_local_sample_len,
+ atomic_read(&perf_sample_allowed_ns),
+ sysctl_perf_event_sample_rate);
+
+ update_perf_cpu_limits();
+}
+
static atomic64_t perf_event_id;
static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ed6c01626ac..f1fa5538610 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1050,6 +1050,15 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = perf_proc_update_handler,
},
+ {
+ .procname = "perf_cpu_time_max_percent",
+ .data = &sysctl_perf_cpu_time_max_percent,
+ .maxlen = sizeof(sysctl_perf_cpu_time_max_percent),
+ .mode = 0644,
+ .proc_handler = perf_cpu_time_max_percent_handler,
+ .extra1 = &zero,
+ .extra2 = &one_hundred,
+ },
#endif
#ifdef CONFIG_KMEMCHECK
{