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 D2954C28CF6 for ; Fri, 3 Aug 2018 19:08:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8FFB921782 for ; Fri, 3 Aug 2018 19:08:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FFB921782 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 S1731738AbeHCVGb (ORCPT ); Fri, 3 Aug 2018 17:06:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58224 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728246AbeHCVGb (ORCPT ); Fri, 3 Aug 2018 17:06:31 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3DA127A7EF; Fri, 3 Aug 2018 19:08:56 +0000 (UTC) Received: from redhat.com (ovpn-117-153.ams2.redhat.com [10.36.117.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id CE9502142F20; Fri, 3 Aug 2018 19:08:52 +0000 (UTC) Date: Fri, 3 Aug 2018 22:08:51 +0300 From: "Michael S. Tsirkin" To: Jason Wang Cc: 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, benh@kernel.crashing.org, 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: <20180803220812-mutt-send-email-mst@kernel.org> References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180802235332-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 03 Aug 2018 19:08:56 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 03 Aug 2018 19:08:56 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.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 10:41:41AM +0800, Jason Wang wrote: > > > On 2018年08月03日 04:55, Michael S. Tsirkin wrote: > > On Fri, Jul 20, 2018 at 09:29:37AM +0530, Anshuman Khandual wrote: > > > This patch series is the follow up on the discussions we had before about > > > the RFC titled [RFC,V2] virtio: Add platform specific DMA API translation > > > for virito devices (https://patchwork.kernel.org/patch/10417371/). There > > > were suggestions about doing away with two different paths of transactions > > > with the host/QEMU, first being the direct GPA and the other being the DMA > > > API based translations. > > > > > > First patch attempts to create a direct GPA mapping based DMA operations > > > structure called 'virtio_direct_dma_ops' with exact same implementation > > > of the direct GPA path which virtio core currently has but just wrapped in > > > a DMA API format. Virtio core must use 'virtio_direct_dma_ops' instead of > > > the arch default in absence of VIRTIO_F_IOMMU_PLATFORM flag to preserve the > > > existing semantics. The second patch does exactly that inside the function > > > virtio_finalize_features(). The third patch removes the default direct GPA > > > path from virtio core forcing it to use DMA API callbacks for all devices. > > > Now with that change, every device must have a DMA operations structure > > > associated with it. The fourth patch adds an additional hook which gives > > > the platform an opportunity to do yet another override if required. This > > > platform hook can be used on POWER Ultravisor based protected guests to > > > load up SWIOTLB DMA callbacks to do the required (as discussed previously > > > in the above mentioned thread how host is allowed to access only parts of > > > the guest GPA range) bounce buffering into the shared memory for all I/O > > > scatter gather buffers to be consumed on the host side. > > > > > > 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 expect he's writing up the data in more detail, but > > just wanted to let you know this would be one more > > thing to debug before we can just switch to DMA APIs. > > > > > > > Anshuman Khandual (4): > > > virtio: Define virtio_direct_dma_ops structure > > > virtio: Override device's DMA OPS with virtio_direct_dma_ops selectively > > > virtio: Force virtio core to use DMA API callbacks for all virtio devices > > > virtio: Add platform specific DMA API translation for virito devices > > > > > > arch/powerpc/include/asm/dma-mapping.h | 6 +++ > > > arch/powerpc/platforms/pseries/iommu.c | 6 +++ > > > drivers/virtio/virtio.c | 72 ++++++++++++++++++++++++++++++++++ > > > drivers/virtio/virtio_pci_common.h | 3 ++ > > > drivers/virtio/virtio_ring.c | 65 +----------------------------- > > > 5 files changed, 89 insertions(+), 63 deletions(-) > > > > > > -- > > > 2.9.3