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Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader

To: Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxxxxxx>
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Tue, 06 Jan 2015 09:39:57 +0100
Cc: Gleb Natapov <gleb@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>
Delivery-date: Tue, 06 Jan 2015 08:40:46 +0000
List-id: Xen developer discussion <xen-devel.lists.xen.org>


On 05/01/2015 20:17, Marcelo Tosatti wrote:
> But there is no guarantee that vCPU-N has updated its pvti when
> vCPU-M resumes guest instruction execution.

You're right.

> So the cost this patch removes is mainly from __getcpu (==RDTSCP?) ?
> Perhaps you can use Gleb's idea to stick vcpu id into version field ?

Or just replace __getcpu with rdtscp.

Paolo

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References:
- Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader
  - From: Marcelo Tosatti
- Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader
  - From: Andy Lutomirski
- Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader
  - From: Marcelo Tosatti

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