diff options
| -rw-r--r-- | Documentation/sysctl/kernel.txt | 26 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/perf_event.c | 12 | ||||
| -rw-r--r-- | include/linux/perf_event.h | 7 | ||||
| -rw-r--r-- | kernel/events/core.c | 92 | ||||
| -rw-r--r-- | kernel/sysctl.c | 9 |
5 files changed, 141 insertions, 5 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index bcff3f9..ab7d16e 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -427,6 +427,32 @@ 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 ab33952..afc2413 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 056f93a..50b3efd 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -706,10 +706,17 @@ 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 9c89207..1db3af9 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); +} static int perf_rotate_context(struct perf_cpu_context *cpuctx); @@ -182,10 +198,78 @@ 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 b0a1f99..4ce13c3 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1043,6 +1043,15 @@ 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 { |