Messages in this thread | | | Date | Thu, 29 Nov 2007 11:57:44 +0100 | From | Ingo Molnar <> | Subject | Re: scheduling anomaly on uml (was: -rt doesn't compile for UML) |
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* Miklos Szeredi <miklos@szeredi.hu> wrote:
> I can't say I'm understading these traces very well, but here's a > snippet that looks a bit strange. I'm running 'while true; do date; > done' in parallel with the dd. > > For some time it is doing 100% CPU as expected, then it goes into a > second or so of mosty idle (afaics), and then returns to the normal > pattern again.
try:
echo 1 > /proc/sys/kernel/stackframe_tracing
to get symbolic stack backdumps for the wakeup points, and add trace_special_sym() calls to generate extra stackdump entries at arbitrary places. schedule() does not have it right now - it might make sense to add it.
also, enabling mcount:
echo 1 > /proc/sys/kernel/mcount_enabled
will give you a _lot_ more verbose trace. Likewise:
echo 1 > /proc/sys/kernel/syscall_tracing
(but for that you'd have to add the sys_call()/sys_ret() instrumentation that x86 has in entry_32.S)
but even this highlevel trace shows something weird:
> events/0-4 0.... 16044512us+: schedule <<idle>-0> (20 -5) > <idle>-0 0.... 16044564us!: schedule <events/0-4> (-5 20) > <idle>-0 0.Nh. 16076072us+: __trace_start_sched_wakeup <date-7133> (120 -1) > <idle>-0 0.Nh. 16076075us+: __trace_start_sched_wakeup <dd-6444> (120 -1) > <idle>-0 0.Nh. 16076078us+: __trace_start_sched_wakeup <kswapd0-33> (115 -1) > dd-6444 0.... 16076104us+: schedule <<idle>-0> (20 0)
how come UML idled for 30 msecs here, while the workload was supposed to be CPU-bound? It's not IO bound anywhere, right? No SMP artifacts either, right?
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