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    SubjectGuest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup
    Booting RHEL 5 i386 in kvm with -no-kvm-irqchip -smp 4 will hang in 
    udev. I bisected this to a change in the _guest_ kernel:

    > commit 95492e4646e5de8b43d9a7908d6177fb737b61f0
    > Author: Ingo Molnar <>
    > Date: Fri Feb 16 01:27:34 2007 -0800
    > [PATCH] x86: rewrite SMP TSC sync code
    > make the TSC synchronization code more robust, and unify it
    > between x86_64 and
    > i386.
    > The biggest change is the removal of the 'fix up TSCs' code on
    > x86_64 and
    > i386, in some rare cases it was /causing/ time-warps on SMP systems.
    > The new code only checks for TSC asynchronity - and if it can prove a
    > time-warp (if it can observe the TSC going backwards when going
    > from one CPU
    > to another within a critical section), then the TSC clock-source
    > is turned
    > off.
    > The TSC synchronization-checking code also got moved into a
    > separate file.

    So, guest kernels prior to this commit will hang in kvm smp; after this
    commit they will boot fine.

    While the change mentions that it fixes a time warp bug, it also says it
    should be rare. So clearly kvm smp tsc handing is buggy. Ingo/Thomas,
    (or anybody else), do you have any insight as to what kvm can be doing
    wrong to trigger this behavior?

    error compiling committee.c: too many arguments to function

     \ /
      Last update: 2007-12-18 18:23    [W:0.022 / U:93.260 seconds]
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