Messages in this thread | | | Subject | Re: Benchmarks of kernel tracing options (ftrace and ktrace) | From | Steven Rostedt <> | Date | Wed, 13 Oct 2010 19:50:30 -0400 |
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On Wed, 2010-10-13 at 16:19 -0700, David Sharp wrote: > Google uses kernel tracing aggressively in the its data centers. We
Thanks!
> wrote our own kernel tracer, ktrace. However ftrace, perf and LTTng > all have a better feature set than ktrace, so we are abandoning that > code.
Cool!
> > We see several implementations of tracing aimed at the mainline kernel > and wanted a fair comparison of each of them to make sure they will > not significantly impact performance. A tracing toolkit that is too > expensive is not usable in our environment. >
[ snip for now (I'm traveling) ]
> This first set of benchmark results compares ftrace to ktrace. The > numbers below are the "on" result minus the "off" result for each > configuration. > > ktrace: 200ns (tracepoint: kernel_getuid) > ftrace: 224ns (tracepoint: timer:sys_getuid) > ftrace: 587ns (tracepoint: syscalls:sys_enter_getuid)
> The last result shows that the syscall tracing is about twice as > expensive as a normal tracepoint, which is interesting.
Argh, the syscall tracing has a lot of overhead. There is only one tracepoint that is hooked into the ptrace code, and will save all registers before calling the functions. It enables tracing on all syscalls and there's a table that decides whether or not to trace the syscall.
So I'm not surprised with the result that the syscall trace point is so slow (note, perf uses the same infrastructure).
-- Steve
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