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authorDave Hansen <dave.hansen@linux.intel.com>2013-06-21 08:51:36 -0700
committerIngo Molnar <mingo@kernel.org>2013-06-23 11:52:57 +0200
commit14c63f17b1fde5a575a28e96547a22b451c71fb5 (patch)
tree781f7327f4341a3d27197e88994b1859e9b51722 /Documentation/trace
parent2ab00456ea8a0d79acb1390659b98416111880b2 (diff)
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>
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