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

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Date:	Tue, 06 Jan 2015 09:39:57 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	Gleb Natapov <gleb@...nel.org>, kvm list <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso
 pvclock reader



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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