From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yaniv Kaul <ykaul@redhat.com>
Subject: Re: [KVM-AUTOTEST][PATCH] timedrift support
Date: Sat, 16 May 2009 23:36:55 +0300
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Cc: Lucas Meneghel Rodrigues <mrodrigu@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>, uril@redhat.com,
	kvm@vger.kernel.org
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On 5/15/2009 7:30 PM, bear wrote:
> Good morning you all. :)
>
> Lucas:
> Very appreciated your help on try...except block implementation. I am 
> finally understand your means when I read the mail.  :(
>
> I modified the timedrift case in several place again.
> 1. add more comments in script.
> 2. functional the snippnet of script which get clock resource from 
> guest and host.
> 3. using vm.get_command_status replace the sendline API when complie 
> the stress program in guest area.
>
> If there is something need to be done by me for the script. feel free 
> just kick me.
>
> Happy weekend.
Hi Bear,

Please drop the NTP stuff. There's no need for it.
Llet me again suggest my algorithm (pseudo-code, of course):

MeasureHostParams() // don't forget to measure the host's CPU, memory, 
I/O and network data - always useful.
while (!enough)
{
     RunAnotherVM() // don't forget to call SleepTillVmIsFullyRunning()
     ForEachVM // this runs in parallel on the VMs
     {
         before = TimeOnHost()
         RunXMinutesLoadOnGuest(load, minutes) // load can vary - 
synthetic CPU, I/O or 'real life' load. Can also vary from VM to VM.
         after = TimeOnHost()
         drift = after - before
         If(drift >= TooMuch) // How much is too much? Could be in 
percentage or absolute values.
             enough = true
     }
}

Simple algorithm, works for us, does not require NTP, and loads the host 
in the most natural way it will be loaded in real life - by more VMs.
Slight variations are possible. For example, use the first VM as a 
'canary' VM - and measure only on it - the others can do random load; 
pin down VM to CPUs; vary the load, the VMs used, and the time, etc.

HTH,
Y.