From mboxrd@z Thu Jan 1 00:00:00 1970 From: dhsharp@google.com (David Sharp) Date: Wed, 17 Nov 2010 15:22:15 -0800 Subject: [ltt-dev] Benchmarks of kernel tracing options 2 (ftrace, lttng and perf) In-Reply-To: <1290034589.4ce45d9d7be28@www.imp.polymtl.ca> References: <1290029498.4ce449ba1679d@www.imp.polymtl.ca> <1290030106.30543.74.camel@gandalf.stny.rr.com> <1290034589.4ce45d9d7be28@www.imp.polymtl.ca> Message-ID: On Wed, Nov 17, 2010 at 2:56 PM, Douglas Santos wrote: > Quoting Steven Rostedt : >> 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. > > >