>-----Original Message-----
>From: [EMAIL PROTECTED] 
>[mailto:[EMAIL PROTECTED] On Behalf Of 
>Ulrich Drepper
>Sent: Friday, August 03, 2007 2:24 AM
>To: Nakajima, Jun
>Cc: kvm-devel@lists.sourceforge.net
>Subject: Re: [kvm-devel] [PATCH 2/2] Add MSR Bitmap support in VMX
>
>-----BEGIN PGP SIGNED MESSAGE-----
>Hash: SHA1
>
>Nakajima, Jun wrote:
>>> Looking at the Linux context switch code, it can bang on MSR_FS_BASE
>> and
>>> MSR_KERNEL_GS_BASE. A high context switch rate between 
>threads (which
>>> use %gs or %fs) can show an improvement with this.  Things 
>like kbuild
>>> probably won't as they use single threaded processes.
>> 
>> Right. 
>
>In Linux there is no difference between single- and multi-threaded
>processes when it comes to setting up segment registers.  Every x86-64
>process uses %fs for TLS and every x86 process uses %gs.  There are
>always variables accessed this way (errno, for instance).
>

I have to say, the benefit form _no_ VMExits on these VMExits are not so
obviously, because each context switch invloves a guest CR3 update, then
a page fault vmexit is triggered and a shadow handling is involved,
which is the major cost of guest context switch.
-Xin 

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