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| author | Dave Hansen <dave.hansen@linux.intel.com> | 2013-06-21 08:51:36 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-06-23 11:52:57 +0200 |
| commit | 14c63f17b1fde5a575a28e96547a22b451c71fb5 (patch) | |
| tree | 781f7327f4341a3d27197e88994b1859e9b51722 /include/linux/perf_event.h | |
| parent | 2ab00456ea8a0d79acb1390659b98416111880b2 (diff) | |
| download | lwn-14c63f17b1fde5a575a28e96547a22b451c71fb5.tar.gz lwn-14c63f17b1fde5a575a28e96547a22b451c71fb5.zip | |
perf: Drop sample rate when sampling is too slow
This patch keeps track of how long perf's NMI handler is taking,
and also calculates how many samples perf can take a second. If
the sample length times the expected max number of samples
exceeds a configurable threshold, it drops the sample rate.
This way, we don't have a runaway sampling process eating up the
CPU.
This patch can tend to drop the sample rate down to level where
perf doesn't work very well. *BUT* the alternative is that my
system hangs because it spends all of its time handling NMIs.
I'll take a busted performance tool over an entire system that's
busted and undebuggable any day.
BTW, my suspicion is that there's still an underlying bug here.
Using the HPET instead of the TSC is definitely a contributing
factor, but I suspect there are some other things going on.
But, I can't go dig down on a bug like that with my machine
hanging all the time.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus@samba.org
Cc: acme@ghostprotocols.net
Cc: Dave Hansen <dave@sr71.net>
[ Prettified it a bit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/perf_event.h')
| -rw-r--r-- | include/linux/perf_event.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 056f93a7990f..50b3efd14d29 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) { |