Messages in this thread | | | From | David Sharp <> | Date | Wed, 17 Nov 2010 15:22:15 -0800 | Subject | Re: Benchmarks of kernel tracing options 2 (ftrace, lttng and perf) |
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On Wed, Nov 17, 2010 at 2:56 PM, Douglas Santos <douglas.santos@polymtl.ca> wrote: > Quoting Steven Rostedt <rostedt@goodmis.org>: >> On Wed, 2010-11-17 at 16:31 -0500, Douglas Santos wrote: >> > Hi all, >> > >> > This is a response to a benchmark, submitted a few weeks ago, comparing >> kernel >> > tracing options. >> > http://lkml.org/lkml/2010/10/28/422 >> > >> > We followed the methodology described in the link bellow, >> > but using the shellscripts posted there to reproduce autotest scripts. >> > http://lkml.org/lkml/2010/10/28/261 >> > >> > We disabled the extra syscall tracing on lttng, for a fair comparison. >> > http://lkml.org/lkml/2010/10/28/290 >> > >> > Average results with tracing "on": >> > >> > lttng: 220 ns >> > ftrace: 260 ns >> >> Heh, so ftrace got worse with the new kernel?
Steve, can you explain how you're drawing that conclusion? Did Douglas run this benchmark before on a previous kernel (I didn't see it if so)?
- You can't directly compare to my results because of different hardware. - The methodology for lttng is different (syscall tracing was removed). - My results were also on 2.6.36
> The previous bench was doing tracing "on" minus "off" > average results. They also used autotest scripts, not sure if > it does exactly the same thing.
I think the subtraction is important, or it is at least important to see what the "off" result is as a baseline of comparison. Otherwise, a huge portion of the measurement is the cost of making the syscall itself.
> > I'll check if we missed something. > > > -- 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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