From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: Seeking a KVM benchmark Date: Mon, 10 Nov 2014 19:38:35 +0200 Message-ID: <20141110173835.GA26770@minantech.com> References: <20141108120125.GB2654@minantech.com> <20141109085238.GA26187@minantech.com> <54608D77.2090907@redhat.com> <20141110104531.GB26187@minantech.com> <5460AC7C.8040409@redhat.com> <5460CA71.2050701@gmail.com> <5460F5B9.8030902@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , Andy Lutomirski , kvm list To: Paolo Bonzini Return-path: Received: from mail-wg0-f42.google.com ([74.125.82.42]:62281 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753292AbaKJRin (ORCPT ); Mon, 10 Nov 2014 12:38:43 -0500 Received: by mail-wg0-f42.google.com with SMTP id k14so9436793wgh.15 for ; Mon, 10 Nov 2014 09:38:38 -0800 (PST) Content-Disposition: inline In-Reply-To: <5460F5B9.8030902@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Nov 10, 2014 at 06:28:25PM +0100, Paolo Bonzini wrote: > 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. > Just a guess, but may be because writing EFER is not something that happens often in regular OSes it is not optimized to handle different bits differently. -- Gleb.