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    SubjectRe: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host
    On Wed, Dec 07, 2011 at 04:41:17PM +0200, Avi Kivity wrote:
    > On 12/05/2011 10:18 PM, Eric B Munson wrote:
    > > Changes from V4:
    > > Add description of KVMCLOCK_GUEST_PAUSED ioctl to api.txt
    > >
    > > Changes from V3:
    > > Include CC's on patch 3
    > > Drop clear flag ioctl and have the watchdog clear the flag when it is reset
    > >
    > > Changes from V2:
    > > A new kvm functions defined in kvm_para.h, the only change to pvclock is the
    > > initial flag definition
    > >
    > > Changes from V1:
    > > (Thanks Marcelo)
    > > Host code has all been moved to arch/x86/kvm/x86.c
    > > KVM_PAUSE_GUEST was renamed to KVM_GUEST_PAUSED
    > >
    > > When a guest kernel is stopped by the host hypervisor it can look like a soft
    > > lockup to the guest kernel. This false warning can mask later soft lockup
    > > warnings which may be real. This patch series adds a method for a host
    > > hypervisor to communicate to a guest kernel that it is being stopped. The
    > > final patch in the series has the watchdog check this flag when it goes to
    > > issue a soft lockup warning and skip the warning if the guest knows it was
    > > stopped.
    > >
    > > It was attempted to solve this in Qemu, but the side effects of saving and
    > > restoring the clock and tsc for each vcpu put the wall clock of the guest behind
    > > by the amount of time of the pause. This forces a guest to have ntp running
    > > in order to keep the wall clock accurate.
    > Having this controlled from userspace means it doesn't work for SIGSTOP
    > or for long scheduling delays. What about doing this automatically
    > based on preempt notifiers?

    Long scheduling delays should be considered hangups from the guest

    About SIGSTOP, that is a corner case. Unsure if its even properly supported
    by QEMU.

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      Last update: 2011-12-14 13:23    [W:0.023 / U:0.752 seconds]
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