On Wed, 2009-01-21 at 16:18 +0100, Ingo Molnar wrote: > * Avi Kivity <avi@xxxxxxxxxx> wrote: > > It means, a scheduling problem. Can you run the latency tracer (which > > only works with realtime priority), so we can tell if it is (a) kvm > > failing to wake up the vcpu properly or (b) the scheduler delaying the > > vcpu from running. > > Could we please get an ftrace capture of the incident? > > Firstly, it makes sense to simplify the tracing environment as much as > possible: for example single-CPU traces are much easier to interpret. > > Can you reproduce it with just one CPU online? I.e. if you offline all the > other cores via: > > echo 0 > /sys/devices/system/cpu/cpu1/online > > [etc.] > > and keep CPU#0 only, do the latencies still occur? > > If they do still occur, then please do the traces that way. > > [ If they do not occur then switch back on all CPUs - we'll sort out the > traces ;-) ] > > Then please build a function tracer kernel, by enabling: > > CONFIG_FUNCTION_TRACER=y > CONFIG_FUNCTION_GRAPH_TRACER=y > CONFIG_DYNAMIC_FTRACE=y Looks like the function graph tracer is only in 2.6.29, so I've updated now to 2.6.29-rc2-00013-gf3b8436. Again, a control test to make sure the problem still occurs: --- hermes-old.wumi.org.au ping statistics --- 64 packets transmitted, 64 received, 0% packet loss, time 63080ms rtt min/avg/max/mdev = 0.168/479.893/4015.950/894.721 ms, pipe 5 Yes, plenty of delays there. Next, checking if I can reproduce with only one core online: echo 0 > /sys/devices/system/cpu/cpu1/online echo 0 > /sys/devices/system/cpu/cpu2/online echo 0 > /sys/devices/system/cpu/cpu3/online ... --- hermes-old.wumi.org.au ping statistics --- 900 packets transmitted, 900 received, 0% packet loss, time 900253ms rtt min/avg/max/mdev = 0.127/38.937/2082.347/170.348 ms, pipe 3 --- hermes-old.wumi.org.au ping statistics --- 900 packets transmitted, 900 received, 0% packet loss, time 900995ms rtt min/avg/max/mdev = 0.127/428.398/17126.227/1634.980 ms, pipe 18 So it looks like I can do the simplified trace. I've run out of time for that this morning, but I'll spend some time on it over the weekend. Thanks for the detailed instructions - it doesn't look like it will be too hard. Cheers, Kevin. -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
