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    SubjectRe: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)
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    On Tue, 2009-01-20 at 15:04 +0200, Avi Kivity wrote:
    > Kevin Shanahan wrote:
    > > On Tue, 2009-01-20 at 12:35 +0100, Ingo Molnar wrote:
    > >> This only seems to occur under KVM, right? I.e. you tested it with -no-kvm
    > >> and the problem went away, correct?
    > >>
    > >
    > > Well, the I couldn't make the test conditions identical, but it the
    > > problem didn't occur with the test I was able to do:
    > >
    > > http://marc.info/?l=linux-kernel&m=123228728416498&w=2
    > >
    > >
    >
    > Can you also try with -no-kvm-irqchip?
    >
    > You will need to comment out the lines
    >
    > /* ISA IRQs map to GSI 1-1 except for IRQ0 which maps
    > * to GSI 2. GSI maps to ioapic 1-1. This is not
    > * the cleanest way of doing it but it should work. */
    >
    > if (vector == 0)
    > vector = 2;
    >
    > in qemu/hw/apic.c (should also fix -no-kvm smp). This will change kvm
    > wakeups to use signals rather than the in-kernel code, which may be buggy.

    Okay, I commented out those lines and compiled a new kvm-82 userspace
    and kernel modules. Using those on a vanilla 2.6.28 kernel, with all
    guests run with -no-kvm-irqchip added.

    As before a number of the XP guests wanted to chug away at 100% CPU
    usage for a long time. Three of the guests clocked up ~40 minutes CPU
    time before I decided to just shut them down. Perhaps coincidentally,
    these three guests are the only ones with Office 2003 installed on them.
    That could be the difference between those guests and the other XP
    guests, but that's probably not important for now.

    The two Linux SMP guests booted okay this time, though they seem to only
    use one CPU on the host (I guess kvm is not multi-threaded in this
    mode?). "hermes-old", the guest I am pinging in all my tests, had a lot
    of trouble running the apache2 setup - it was so slow it was difficult
    to load a complete page from our RT system. The kvm process for this
    guest was taking up 100% cpu on the host constantly and all sorts of
    wierd stuff could be seen by watching top in the guest:

    top - 03:44:17 up 43 min, 1 user, load average: 3.95, 1.55, 0.80
    Tasks: 101 total, 4 running, 97 sleeping, 0 stopped, 0 zombie
    Cpu(s): 79.7%us, 10.4%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 9.9%si,
    0.0%st
    Mem: 2075428k total, 391128k used, 1684300k free, 13044k buffers
    Swap: 3502160k total, 0k used, 3502160k free, 118488k cached
    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    2956 postgres 20 0 19704 11m 10m S 1658 0.6 2:55.99 postmaster
    2934 www-data 20 0 60392 40m 5132 R 31 2.0 0:17.28 apache2
    2958 postgres 20 0 19700 11m 9.8m R 28 0.6 0:20.41 postmaster
    2940 www-data 20 0 58652 38m 5016 S 27 1.9 0:04.87 apache2
    2937 www-data 20 0 60124 40m 5112 S 18 2.0 0:11.00 apache2
    2959 postgres 20 0 19132 5424 4132 S 10 0.3 0:01.50 postmaster
    2072 postgres 20 0 8064 1416 548 S 7 0.1 0:23.71 postmaster
    2960 postgres 20 0 19132 5368 4060 R 6 0.3 0:01.55 postmaster
    2071 postgres 20 0 8560 1972 488 S 5 0.1 0:08.33 postmaster

    Running the ping test with without apache2 running in the guest:

    --- hermes-old.wumi.org.au ping statistics ---
    900 packets transmitted, 900 received, 0% packet loss, time 902740ms
    rtt min/avg/max/mdev = 0.568/3.745/272.558/16.990 ms

    And with apache2 running:

    --- hermes-old.wumi.org.au ping statistics ---
    900 packets transmitted, 900 received, 0% packet loss, time 902758ms
    rtt min/avg/max/mdev = 0.625/25.634/852.739/76.586 ms

    In both cases it's quite variable, but the max latency is still not as
    bad as when running with the irq chip enabled.

    Anyway, the test is again not ideal, but I hope we're proving something.
    That's all I can do for tonight - should be ready for more again
    tomorrow night.

    Regards,
    Kevin.




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