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Re: [Qemu-devel] [Bug 992067] Re: Windows 2008R2 very slow cold boot whe

From: Owen Tuz
Subject: Re: [Qemu-devel] [Bug 992067] Re: Windows 2008R2 very slow cold boot when >4GB memory
Date: Mon, 23 Jul 2012 12:07:02 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

We have been experiencing this problem for a while now too, using qemu-kvm 
(currently at 1.1.1). 

Unfortunately, hv_relaxed doesn't seem to fix it. The following command line 
produces the issue:

qemu-kvm -nodefaults -m 4096 -smp 8 -cpu host,hv_relaxed -vga cirrus -usbdevice 
tablet -vnc :99 -monitor stdio -hda

The hardware consists of dual AMD Opteron 6128 processors (16 cores in total) 
and 64GB of memory. This command line was tested on kernel 3.1.4. 

I've also tested with -no-hpet.

What I have seen is much as described: the memory fills out slowly, and top on 
the host will show the process using
100% on all allocated CPU cores. The most extreme case was a machine which took 
something between 6 and 8 hours to boot.

This seems to be related to the assigned memory, as described, but also the 
number of processor cores (which makes
sense if we believe it's a timing issue?). I have seen slow-booting guests 
improved by switching down to a single or even two cores.

Matthew, I agree that this seems to be linked to the number of VMs running - in 
fact, shutting down other VMs on a dedicated test host caused the machine to 
start booting at a normal speed (with no reboot required).

However, the level of contention is never such that this could be explained by 
the host simply being overcommitted.

If it helps anyone, there's an image of the hard drive I've been using to test 

It's 5G of gzip file containing a fairly standard Windows 2008 trial 
installation. Since it's in the trial period, anyone who wants to use it may 
have to re-arm the trial: http://support.microsoft.com/kb/948472 

Please let me know if I can provide any more information, or test anything.

Best wishes,

Owen Tuz

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