Messages in this thread |  | | | Subject | Re: Tracing configuration review | | From | Chase Douglas <> | | Date | Tue, 25 May 2010 15:58:18 -0400 |
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On Tue, 2010-05-25 at 15:46 -0400, Steven Rostedt wrote: > On Tue, 2010-05-25 at 15:31 -0400, Chase Douglas wrote: > > Hi all, > > > > I'm going through our Ubuntu kernel configuration for our next release > > to ensure we have all the trace options enabled that may be useful. I > > have a few questions about what tracer options we should have enabled. > > > > Our guiding principle in regards to these options is: if an option can > > be turned on and has no performance impact unless explicitly enabled on > > the kernel command line or at runtime, we are happy to enable it. > > Secondarily, we don't want to enable options that are headed for > > deprecation. > > > > The following options are what I am looking to set for our x86 > > configurations. I've only included those that I am not 100% sure of. > > Comments are what I could gather from documentation and Kconfig, but > > they may not be accurate: > > > > # CONFIG_IRQSOFF_TRACER is not set (performance impact by default) > > Correct, keep that off. > > > # CONFIG_SYSPROF_TRACER is not set (don't know much about this) > > Neither do I ;-) > > > > # CONFIG_SCHED_TRACER is not set (headed for deprecation?) > > Although it is headed for deprecation, I think it still gets set by > other tracers, since it has the code to initiate the comm reader. > > > CONFIG_FTRACE_SYSCALLS=y (no performance impact by default) > > Correct > > > CONFIG_BOOT_TRACER=y (no performance impact by default) > > But this tracer is pretty useless. It gives no more information than > debug_initcalls. > > > CONFIG_KSYM_TRACER=y (no performance impact by default) > > Yep > > > # CONFIG_STACK_TRACER is not set (Kconfig says N if unsure) > > I would set this if you already have the function tracer. It gives no > more overhead than that, and it is very useful. > > > # CONFIG_KMEMTRACE is not set (Kconfig says N if unsure) > > Don't know. > > > CONFIG_WORKQUEUE_TRACER=y (no performance impact by default) > > > > Lastly, what options are safe for performance when > > HAVE_DYNAMIC_FTRACE=n, like on our ARM kernels. It is not clear to me > > through what's in Documentation/trace/* and the Kconfig entries what > > options could cause a performance decrease due to the inability to > > dynamically enable and disable tracing at runtime. > > HAVE_DYNAMIC_FTRACE affects the function tracer. If you do not have > that, then do not enable FUNCTION_TRACER or anything that depends on it. > > Also note, FUNCTION_TRACER depends on FRAME_POINTERS. Your millage may > vary with that. If you already have FRAME_POINTERS on, and the arch > supports DYNAMIC_FTRACE, then its fine to have FUNCTION_TRACER and all > those that are built on top (STACK_TRACER, FUNCTION_GRAPH, etc)
(I would have snipped much of the above, but since I've added CC for the Ubuntu list I wanted to leave it as is for this first reply)
After enabling KSYM_TRACER, I was presented with PROFILE_KSYM_TRACER. This is also "Say N if unsure," so I could use some guidance on whether we should turn it on as well.
Thanks,
-- Chase
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