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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 55FA2C4646D for ; Sun, 5 Aug 2018 00:24:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1CD7B217CE for ; Sun, 5 Aug 2018 00:24:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1CD7B217CE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730169AbeHEC1D (ORCPT ); Sat, 4 Aug 2018 22:27:03 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:33080 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727350AbeHEC1D (ORCPT ); Sat, 4 Aug 2018 22:27:03 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0A03840203F2; Sun, 5 Aug 2018 00:24:33 +0000 (UTC) Received: from redhat.com (ovpn-116-17.ams2.redhat.com [10.36.116.17]) by smtp.corp.redhat.com (Postfix) with SMTP id 2FCE210F1C0B; Sun, 5 Aug 2018 00:24:29 +0000 (UTC) Date: Sun, 5 Aug 2018 03:24:28 +0300 From: "Michael S. Tsirkin" To: Benjamin Herrenschmidt Cc: Jason Wang , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, mpe@ellerman.id.au, hch@infradead.org, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180805032355-mutt-send-email-mst@kernel.org> References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180802235332-mutt-send-email-mst@kernel.org> <20180803220812-mutt-send-email-mst@kernel.org> <01c74680c4b3aa25d9b4375a9ab5e10046b7c71b.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <01c74680c4b3aa25d9b4375a9ab5e10046b7c71b.camel@kernel.crashing.org> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Sun, 05 Aug 2018 00:24:33 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Sun, 05 Aug 2018 00:24:33 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mst@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 03, 2018 at 08:21:26PM -0500, Benjamin Herrenschmidt wrote: > On Fri, 2018-08-03 at 22:08 +0300, Michael S. Tsirkin wrote: > > > > > Please go through these patches and review whether this approach broadly > > > > > makes sense. I will appreciate suggestions, inputs, comments regarding > > > > > the patches or the approach in general. Thank you. > > > > > > > > Jason did some work on profiling this. Unfortunately he reports > > > > about 4% extra overhead from this switch on x86 with no vIOMMU. > > > > > > The test is rather simple, just run pktgen (pktgen_sample01_simple.sh) in > > > guest and measure PPS on tap on host. > > > > > > Thanks > > > > Could you supply host configuration involved please? > > I wonder how much of that could be caused by Spectre mitigations > blowing up indirect function calls... > > Cheers, > Ben. I won't be surprised. If yes I suggested a way to mitigate the overhead. -- MSR