Messages in this thread | | | Date | Tue, 16 Nov 2010 15:28:44 -0500 | From | Mathieu Desnoyers <> | Subject | Re: Benchmarks of kernel tracing options (ftrace, ktrace, lttng and perf) |
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* David Sharp (dhsharp@google.com) wrote: [...] > Results for amount of time to execute a tracepoint (includes previous results): > ktrace: 200ns (old) > ftrace: 224ns (old, w/ handcoded tracepoint, not syscall tracing) > lttng: 449ns (new) > perf: 1047ns (new) > > Also interesting: > ftrace: 587ns (old, w/ syscall tracing) > This just shows that syscall tracing is much slower than a normal tracepoint.
As I pointed out in my email a few weeks ago, the LTTng comparison is simply bogus because the "syscall tracing" thread-flag is active, which calls into syscall tracing, after saving all registers, from entry_*.S, both at syscall entry and exit.
I did benchmarks using Steven's ring_buffer_benchmark kernel module, which calls tracing in a loop, for both Ftrace and the Generic Ring Buffer (which is derived from LTTng). The results are:
Intel Xeon 2.0GHz
ftrace: 103 ns/entry (no reader) lttng: 83 ns/entry (no reader) (with the generic ring buffer library)
So, given that even after I pointed out that the results above were bogus, people took the numbers for granted, and given that David seems busy on other things, I thought I should set records straight.
Thanks,
Mathieu
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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