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Re: [Qemu-devel] [PULL 17/19] target-i386: Support "invariant tsc" flag


From: Marcelo Tosatti
Subject: Re: [Qemu-devel] [PULL 17/19] target-i386: Support "invariant tsc" flag
Date: Fri, 8 Aug 2014 18:42:26 -0300
User-agent: Mutt/1.5.21 (2010-09-15)

Chen Liang,

On Fri, Aug 08, 2014 at 07:07:59AM +0000, chenliang (T) wrote:
> Hi,
> We found that value of host cpus tsc are same to echo other when host has 
> invariant tsc flag.

What you mean exactly?

Do you have a test program?

> But it is not in vm. The problem is that offset of vcpus tsc are not equal. 
> The offset is set when
> vcpu is created. Is it ok to set same offset? And is it reasonable?
> 
> Best regards
> Chen Liang


The code at kvm_write_tsc(), in the kernel (arch/x86/kvm/x86.c), should 
adjust the vcpu tsc offsets properly resulting in cross SMP TSCs being
equal in the VM.




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