From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: Seeking a KVM benchmark Date: Mon, 10 Nov 2014 18:28:25 +0100 Message-ID: <5460F5B9.8030902@redhat.com> References: <545C7222.4070605@redhat.com> <20141108120125.GB2654@minantech.com> <20141109085238.GA26187@minantech.com> <54608D77.2090907@redhat.com> <20141110104531.GB26187@minantech.com> <5460AC7C.8040409@redhat.com> <5460CA71.2050701@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Andy Lutomirski , kvm list To: Avi Kivity , Gleb Natapov Return-path: Received: from mail-wg0-f44.google.com ([74.125.82.44]:54046 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752886AbaKJR2e (ORCPT ); Mon, 10 Nov 2014 12:28:34 -0500 Received: by mail-wg0-f44.google.com with SMTP id x12so9446707wgg.17 for ; Mon, 10 Nov 2014 09:28:33 -0800 (PST) In-Reply-To: <5460CA71.2050701@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 10/11/2014 15:23, Avi Kivity wrote: > It's not surprising [1]. Since the meaning of some PTE bits change [2], > the TLB has to be flushed. In VMX we have VPIDs, so we only need to flush > if EFER changed between two invocations of the same VPID, which isn't the > case. > > [1] after the fact > [2] although those bits were reserved with NXE=0, so they shouldn't have > any TLB footprint You're right that this is not that surprising after the fact, and that both Sandy Bridge and Ivy Bridge have VPIDs (even the non-Xeon ones). This is also why I'm curious about the Nehalem. However note that even toggling the SCE bit is flushing the TLB. The NXE bit is not being toggled here! That's the more surprising part. Paolo