From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D318BC432C2 for ; Mon, 23 Sep 2019 23:43:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B24AD2190F for ; Mon, 23 Sep 2019 23:43:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391195AbfIWXnL (ORCPT ); Mon, 23 Sep 2019 19:43:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55504 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729316AbfIWXnK (ORCPT ); Mon, 23 Sep 2019 19:43:10 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 798F1300CB25; Mon, 23 Sep 2019 23:43:10 +0000 (UTC) Received: from mail (ovpn-120-159.rdu2.redhat.com [10.10.120.159]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D1E925D9CA; Mon, 23 Sep 2019 23:43:07 +0000 (UTC) Date: Mon, 23 Sep 2019 19:43:07 -0400 From: Andrea Arcangeli To: Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , "Dr. David Alan Gilbert" , Marcelo Tosatti , Peter Xu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers Message-ID: <20190923234307.GG19996@redhat.com> References: <20190920212509.2578-1-aarcange@redhat.com> <20190920212509.2578-16-aarcange@redhat.com> <87o8zb8ik1.fsf@vitty.brq.redhat.com> <7329012d-0b3b-ce86-f58d-3d2d5dc5a790@redhat.com> <20190923190514.GB19996@redhat.com> <20190923202349.GL18195@linux.intel.com> <20190923210838.GA23063@redhat.com> <20190923212435.GO18195@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190923212435.GO18195@linux.intel.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Mon, 23 Sep 2019 23:43:10 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 23, 2019 at 02:24:35PM -0700, Sean Christopherson wrote: > An extra CALL+RET isn't going to be noticeable, especially on modern > hardware as the high frequency VMWRITE/VMREAD fields should hit the > shadow VMCS. In your last email with regard to the inlining optimizations made possible by the monolithic KVM model you said "That'd likely save a few CALL/RET/JMP instructions", that kind of directly contradicts the above. I think neither one if taken at face value can be possibly measured. However the above only is relevant for nested KVM so I'm fine if there's an agreement that it's better to hide the nested vmx handlers in nested.c at the cost of some call/ret. >From my part I'm dropping 15/16/17 in the short term, perhaps Vitaly or you or Paolo if he has time, want to work on that part in parallel to the orthogonal KVM monolithic changes? Thanks, Andrea