Messages in this thread | | | Date | Fri, 6 Jul 2007 22:35:11 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [patch 10/10] Scheduler profiling - Use immediate values |
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* Adrian Bunk (bunk@stusta.de) wrote: > On Fri, Jul 06, 2007 at 07:43:15PM -0400, Mathieu Desnoyers wrote: > > * Adrian Bunk (bunk@stusta.de) wrote: > > > On Fri, Jul 06, 2007 at 06:14:10PM -0400, Chuck Ebbert wrote: > > > > On 07/06/2007 07:44 AM, Andi Kleen wrote: > > > > > I think the optimization is a good idea, although i dislike it > > > > > that it is complicated for the dynamic markers. If it was just > > > > > static it would be much simpler. > > > > > > > > Another thing to consider is that there might be hundreds of these > > > > probes/tracepoints active in an instrumented kernel. The overhead > > > > adds up fast, so the gain may be worth all the pain. > > > > > > Only if you want to squeeze the last bit of performance out of > > > _debugging_ functionality. > > > > > > You avoid all the pain if you simply don't use debugging functionality > > > on production systems. > > > > > > > Adrian, > > > > Please have a look at my markers posts, especially: > > > > http://www.ussg.iu.edu/hypermail/linux/kernel/0707.0/0669.html > > > > And also look into OLS 2007 proceedings for Martin Bligh's paper on > > Debugging Google sized clusters. It basically makes the case for adding > > functionnality to debug _user space_ problems on production systems that > > can be turned on dynamically. > > Using a different kernel for tracing still fulfills all the requirements > listed in section 5 of your paper... >
Not exactly. I assume you understand that rebooting 1000 live production servers to find the source of a rare bug or the cause of a performance issue is out of question.
Moreover, strategies like enabling flight recorder traces on a few nodes on demand to detect performance problems can only be deployed in production environment if they are part of the standard production kernel.
Also, managing two different kernels is often out of question. Not only is it a maintainance burden, but just switching to the "debug" kernel can impact the system's behavior so badly that it could make the problem disappear.
Mathieu
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - 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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