> > 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.
Umm, trace_special_sym() is ifdefed out, because UML doesn't have save_stack_trace(). > 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) I'll have a look. > 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? Yes. The UML kernel is UP, and I don't think 'date' or 'bash' want to do any disk I/O. Could disk I/O be blocking the tty? I think UML uses separate threads for these, but I don't know the details. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/