Messages in this thread | | | Date | Fri, 18 Jul 2008 10:41:52 +0200 | From | Ingo Molnar <> | Subject | Re: [git pull] tracing fixes |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> On Thu, 17 Jul 2008, Ingo Molnar wrote: > > > > Ingo Molnar (4): > > ftrace: fix merge buglet > > ftrace: fix lockup with MAXSMP > > ftrace: do not trace scheduler functions > > ftrace: do not trace library functions > > > > [...] > > --- a/kernel/Makefile > > +++ b/kernel/Makefile > > @@ -11,8 +11,6 @@ obj-y = sched.o fork.o exec_domain.o panic.o printk.o profile.o \ > > hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \ > > notifier.o ksysfs.o pm_qos_params.o sched_clock.o > > > > -CFLAGS_REMOVE_sched.o = -mno-spe > > - > > ifdef CONFIG_FTRACE > > # Do not trace debug files and internal ftrace files > > CFLAGS_REMOVE_lockdep.o = -pg > > @@ -21,6 +19,7 @@ CFLAGS_REMOVE_mutex-debug.o = -pg > > CFLAGS_REMOVE_rtmutex-debug.o = -pg > > CFLAGS_REMOVE_cgroup-debug.o = -pg > > CFLAGS_REMOVE_sched_clock.o = -pg > > +CFLAGS_REMOVE_sched.o = -mno-spe -pg > > endif > > > > Ingo, > > Why not trace the scheduler functions? I found a lot of useful > information from seeing what functions are being called (namely the > latencies caused by the fair scheduler balancing). Not being able to > trace sched.c seems to keep a lot of useful data from being accessed.
i agree in general, but it was causing lockups with:
http://redhat.com/~mingo/misc/config-Thu_Jul_17_13_34_52_CEST_2008
note the MAXSMP in the config which sets NR_CPUS to 4096:
CONFIG_NR_CPUS=4096
our randconfig testing stumbled on it. That is a debug helper to "tune up the kernel for as large systems as possible" and can bring in regressions not normally seen.
after i spent a good 4 hours on figuring out the lib/*.o details i didnt have the stamina to find the exact reason within sched.o :-)
One thing that needs looking at is that ftrace's self-recursion checks are not as robust as they used to be, and this is a recent regression (as in: last 1-2 weeks). Why do we have to exclude tsc.o from tracing for example? Why isnt cpu_clock() called inside a recursion-protected section? Why are all the trace function callbacks called outside of recursion checks? Why arent ftrace lockups debuggable via the NMI watchdog + early printk? I think it would be more robust to do a recursion check ASAP.
> also, is the '-mno-spe' safe when ftrace is not configured?
Why was the -mno-spe added exactly? I havent seen it explained in the commit that added its removal:
| commit 6ec562328fda585be2d7f472cfac99d3b44d362a | Author: Steven Rostedt <rostedt@goodmis.org> | Date: Wed May 14 21:30:30 2008 -0400 | | ftrace: use the new kbuild CFLAGS_REMOVE for kernel directory
it talks about a cleanup but also adds -mno-spe removal that wasnt there before. This seems to be a powerpc special and the exact context is not clear to me.
Ingo
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