Not the author but maybe I can comment.
On 2013/11/25 08:14:47, Yang wrote:
Up till now we use a wrapper script (tools/run-llprof.sh) to run perf. I
wonder
whether you can simply update it. What's the difference between "-e
cycles"
and
"-g"? Also, the script increases the kernel limit on sampling rate so
that we
don't have missing ticks. Is this still necessary?
-e cycles collects CPU cycles, -g call graphs (in other words: one collects
events, the other metadata.)
Upping the sampling rate with -c is a good idea; the default is 4k and
that's
arguably a little on the low side.
I don't know if the suggestion to increase
kernel.perf_event_max_sample_rate is
all that valuable. It defaults to 100k, which means you can record one
sample
every 10 us. You'd increase that when sampling at a rate of > 100k
samples/sec
but the script samples at 25k samples/sec IIRC and most systems are
probably not
fast enough to keep up anyway.
https://codereview.chromium.org/70013002/
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