Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernelsprior to tsc sync cleanup

2007-12-19 Thread Dor Laor 
Amit Shah wrote:

 On Wednesday 19 December 2007 21:02:06 Glauber de Oliveira Costa wrote:
  On Dec 19, 2007 12:27 PM, Avi Kivity [EMAIL PROTECTED] wrote:
   Ingo Molnar wrote:
* Avi Kivity [EMAIL PROTECTED] wrote:
Avi Kivity wrote:
 Testing shows wrmsr and rdtsc function normally.
   
I'll try pinning the vcpus to cpus and see if that helps.
   
It does.
   
do we let the guest read the physical CPU's TSC? That would be 
 trouble.
  
   vmx (and svm) allow us to add an offset to the physical tsc.  We 
 set it
   on startup to -tsc (so that an rdtsc on boot would return 0), and
   massage it on vcpu migration so that guest rdtsc is monotonic.
  
   The net effect is that tsc on a vcpu can experience large forward 
 jumps
   and changes in rate, but no negative jumps.
 
  Changes in rate does not sound good. It's possibly what's screwing up
  my paravirt clock implementation in smp.

 Do you mean in the case of VM migration, or just starting them on a single
 host?

It's the cpu preemption stuff on local host and not VM migration

  Since the host updates guest time prior to putting vcpu to run, two
  vcpus that start running at different times will have different system
  values.
 
  Now if the vcpu that started running later probes the time first,
  we'll se the time going backwards. A constant tsc rate is the only way
  around
  my limited mind sees around the problem (besides, obviously, _not_
  making the system time per-vcpu).

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Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernelsprior to tsc sync cleanup

2007-12-19 Thread Avi Kivity 
Dor Laor wrote:
  
   vmx (and svm) allow us to add an offset to the physical tsc.  We 
 set it
   on startup to -tsc (so that an rdtsc on boot would return 0), and
   massage it on vcpu migration so that guest rdtsc is monotonic.
  
   The net effect is that tsc on a vcpu can experience large forward 
 jumps
   and changes in rate, but no negative jumps.
 
  Changes in rate does not sound good. It's possibly what's screwing up
  my paravirt clock implementation in smp.

 Do you mean in the case of VM migration, or just starting them on a 
 single
 host?

 It's the cpu preemption stuff on local host and not VM migration

No, migrating a vcpu to another cpu.

-- 
error compiling committee.c: too many arguments to function


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