From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: Seeking a KVM benchmark Date: Mon, 17 Nov 2014 13:22:03 +0100 Message-ID: <5469E86B.6010007@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> <5460F5B9.8030902@redhat.com> <5469D934.4080405@gmail.com> <5469D974.4030008@redhat.com> <5469E361.60308@gmail.com> <5469E43F.5090301@redhat.com> <5469E69B.7050406@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Andy Lutomirski , kvm list To: Wanpeng Li , Avi Kivity , Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:40436 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750806AbaKQMWN (ORCPT ); Mon, 17 Nov 2014 07:22:13 -0500 In-Reply-To: <5469E69B.7050406@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 17/11/2014 13:14, Wanpeng Li wrote: >> >>> Sorry, maybe I didn't state my question clearly. As Avi mentioned above >>> "In VMX we have VPIDs, so we only need to flush if EFER changed between >>> two invocations of the same VPID", so there is only one VPID if the >>> guest is UP, my question is if there need a TLB flush when guest's EFER >>> has been changed? >> Yes, because the meaning of the page table entries has changed. > > So both VMX EFER writes and non-VMX EFER writes cause a TLB flush for UP > guest, is there still a performance improvement in this case? Note that the guest's EFER does not change, so no TLB flush happens. The guest EFER, however, is different from the host's, so if you change it with a wrmsr in the host you will get a TLB flush on every userspace exit. Paolo