path: root/kernel/sysctl.c
diff options
authorDave Hansen <>2013-06-21 15:51:36 (GMT)
committerGreg Kroah-Hartman <>2014-06-11 19:03:26 (GMT)
commit3cd49fd7da79541a1e87bfa5750f5a939c6626df (patch)
tree3263448f7a463b126c4ae6250e8da3d10dd906a0 /kernel/sysctl.c
parent553e4c5591f1e94519ca299aec0c1576f5cede9f (diff)
perf: Drop sample rate when sampling is too slow
commit 14c63f17b1fde5a575a28e96547a22b451c71fb5 upstream. 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 <> Acked-by: Peter Zijlstra <> Cc: Cc: Cc: Dave Hansen <> [ Prettified it a bit. ] Signed-off-by: Ingo Molnar <> Cc: Weng Meiling <> Signed-off-by: Greg Kroah-Hartman <>
Diffstat (limited to 'kernel/sysctl.c')
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ed6c016..f1fa553 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,
+ },