Messages in this thread | | | Date | Mon, 8 Mar 2010 10:31:36 +0800 | Subject | Re: 2.6.33: ftrace triggers soft lockup | From | Américo Wang <> |
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On Fri, Mar 5, 2010 at 11:06 PM, Steven Rostedt <rostedt@goodmis.org> wrote: > On Fri, 2010-03-05 at 15:16 +0800, Américo Wang wrote: >> On Fri, Mar 5, 2010 at 12:14 PM, Américo Wang <xiyou.wangcong@gmail.com> wrote: >> > On Thu, Mar 4, 2010 at 9:54 PM, Steven Rostedt <rostedt@goodmis.org> wrote: >> >> On Wed, 2010-03-03 at 14:04 +0800, Américo Wang wrote: >> >>> I am not sure if this is ftrace's fault, but it is ftrace who triggers >> >>> the soft lockup. On my machine, it is pretty easy, just run: >> >>> >> >>> echo function_graph > current_tracer >> >>> > >> > >> > I can't say that because I didn't try -rc6. >> > >> >> Sigh, 2.6.33-rc6 doesn't work, even 2.6.32 doesn't work... > > So basically you are saying that the function_graph tracer, when enabled > has a high overhead? Well, unfortunately, that's expected.
A unusable system is expected? ;-) Here my machine is too slow to use.
> > So my question to you is, have you seen the function graph perform > better with the same configs in previous kernels? Also, the function > graph makes other debugging (like lockdep) have a greater impact to > performance than they usually do.
Oh, sorry, I still don't find a working kernel, I will try today.
> > Now some things you can do to help performance. One is not to trace > functions that are known to have a high hit rate. You can do this with > the set_ftrace_notrace file, or add "ftrace_notrace=func1,func2,func3" > to the command line where func1,func2,func3 are the functions you do not > want to trace. This just adds these by default to the set_ftrace_notrace > and can be removed at runtime. > > > The functions I commonly write to are: > > echo '*spin_lock*' '*spin_unlock*' '*spin_try*' '*rcu_read*' > set_ftace_notrace > > since these functions are hit quite intensively, by not tracing them it > helps a bit with performance.
I will try this now.
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