[Qemu-devel] timer issue on 1.7.0 and later

[Rob Herring]

I've bisected a problem with system emulation and SMP kernels using
per cpu timers to this commit. I can reproduce this problem on ARM
emulation with both ARM generic timers (only in 1.7.0) and ARM MPCore
timers. Using a single broadcast timer in the guest kernel works fine.
 My host is ubuntu 13.10.

commit b1bbfe72ec1ebf302d97f886cc646466c0abd679
Author: Alex Bligh <address@hidden>
Date:   Wed Aug 21 16:02:55 2013 +0100

    aio / timers: On timer modification, qemu_notify or aio_notify

    On qemu_mod_timer_ns, ensure qemu_notify or aio_notify is called to
    end the appropriate poll(), irrespective of use_icount value.

    On qemu_clock_enable, ensure qemu_notify or aio_notify is called for
    all QEMUTimerLists attached to the QEMUClock.

    Signed-off-by: Alex Bligh <address@hidden>
    Signed-off-by: Stefan Hajnoczi <address@hidden>


This can be reproduced with a simple busybox initramfs and spawning
several instances of a simple shell script to load the cores:

while [ 1 ]; do echo rob > /dev/null; done &

The symptom is user interaction become sluggish and jerky, and then
kernel messages about soft lockup, rcu stalls and/or like this:

hrtimer: interrupt took 3030033000 ns
[sched_delayed] sched: RT throttling activated

I also intermittently hang on boot hitting this warning:

[    0.640204] WARNING: CPU: 0 PID: 0 at
/home/rob/proj/git/linux-2.6/kernel/time/clockevents.c:212
clockevents_program_event+0x50/0x138()

which is from here:

if (unlikely(expires.tv64 < 0)) {
WARN_ON_ONCE(1);
return -ETIME;
}

I'm not sure if this warning is caused by the same commit or not, but
it seems like I'm getting wrong timer values from qemu.


It appears to me that this bug report may also be related:

https://bugs.launchpad.net/qemu/+bug/1222034

Rob