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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 AD3A4C33CA1 for ; Mon, 20 Jan 2020 08:44:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 842782077C for ; Mon, 20 Jan 2020 08:44:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bY+YZNNZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726991AbgATIoR (ORCPT ); Mon, 20 Jan 2020 03:44:17 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:56992 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725872AbgATIoR (ORCPT ); Mon, 20 Jan 2020 03:44:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579509855; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NaXsioYjljuVY6jZb4aFMxl3jkckcuLg1JicxfVLDqk=; b=bY+YZNNZR7kqxotMZLFNxFshZfuQwpll3OmWdIUXznhwqCEEl5LUyl9KIb7LvjaGWsIhls gQ6Rqe9YXfoznJOFdMIoBP28rb45SiqPHGh2jmdg0gxSK5PphP0uoK9USa0A7GsxWz5UHE BnZ1DQ43AxTWJqoT0J00M7uOqr2mG/M= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-264-bGkbTfTSOqe8wSHGCrl1cw-1; Mon, 20 Jan 2020 03:44:14 -0500 X-MC-Unique: bGkbTfTSOqe8wSHGCrl1cw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E3508800D50; Mon, 20 Jan 2020 08:44:11 +0000 (UTC) Received: from [10.72.12.173] (ovpn-12-173.pek2.redhat.com [10.72.12.173]) by smtp.corp.redhat.com (Postfix) with ESMTP id C7B53272A1; Mon, 20 Jan 2020 08:43:55 +0000 (UTC) Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus To: Shahaf Shuler , Rob Miller Cc: "Michael S. Tsirkin" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , Netdev , "Bie, Tiwei" , Jason Gunthorpe , "maxime.coquelin@redhat.com" , "Liang, Cunming" , "Wang, Zhihong" , "Wang, Xiao W" , "haotian.wang@sifive.com" , "Zhu, Lingshan" , "eperezma@redhat.com" , "lulu@redhat.com" , Parav Pandit , "Tian, Kevin" , "stefanha@redhat.com" , "rdunlap@infradead.org" , "hch@infradead.org" , Ariel Adam , "jakub.kicinski@netronome.com" , Jiri Pirko , "hanand@xilinx.com" , "mhabets@solarflare.com" References: <20200116124231.20253-1-jasowang@redhat.com> <20200116124231.20253-4-jasowang@redhat.com> <20200117070324-mutt-send-email-mst@kernel.org> <239b042c-2d9e-0eec-a1ef-b03b7e2c5419@redhat.com> From: Jason Wang Message-ID: Date: Mon, 20 Jan 2020 16:43:53 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/1/19 =E4=B8=8B=E5=8D=885:07, Shahaf Shuler wrote: > Friday, January 17, 2020 4:13 PM, Rob Miller: > Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus >>> On 2020/1/17 =E4=B8=8B=E5=8D=888:13, Michael S. Tsirkin wrote: >>>> On Thu, Jan 16, 2020 at 08:42:29PM +0800, Jason Wang wrote: > [...] > >>>> + * @set_map:=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0= =C2=A0 =C2=A0 =C2=A0 =C2=A0 Set device memory mapping, optional >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 and only needed for device that using >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 device specific DMA translation >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 (on-chip IOMMU) >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 @vdev: vdpa device >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 @iotlb: vhost memory mapping to be >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 used by the vDPA >>>> + *=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 Returns integer: success (0) or error (< 0) >>> OK so any change just swaps in a completely new mapping? >>> Wouldn't this make minor changes such as memory hotplug >>> quite expensive? > What is the concern? Traversing the rb tree or fully replace the on-chi= p IOMMU translations? > If the latest, then I think we can take such optimization on the driver= level (i.e. to update only the diff between the two mapping). This is similar to the design of platform IOMMU part of vhost-vdpa. We=20 decide to send diffs to platform IOMMU there. If it's ok to do that in=20 driver, we can replace set_map with incremental API like map()/unmap(). Then driver need to maintain rbtree itself. > If the first one, then I think memory hotplug is a heavy flow regardles= s. Do you think the extra cycles for the tree traverse will be visible in= any way? I think if the driver can pause the DMA during the time for setting up=20 new mapping, it should be fine. > =20 > >> My understanding is that the incremental updating of the on chip IOMMU >> may degrade the=C2=A0 performance. So vendor vDPA drivers may want to = know >> all the mappings at once. > Yes exact. For Mellanox case for instance many optimization can be perf= ormed on a given memory layout. > >> Technically, we can keep the incremental API >> here and let the vendor vDPA drivers to record the full mapping >> internally which may slightly increase the complexity of vendor driver= . > What will be the trigger for the driver to know it received the last ma= pping on this series and it can now push it to the on-chip IOMMU? For GPA->HVA(HPA) mapping, we can have flag for this. But for GIOVA_>HVA(HPA) mapping which could be changed by guest, it=20 looks to me there's no concept of "last mapping" there. I guess in this=20 case, mappings needs to be set from the ground. This could be expensive=20 but consider most application uses static mappings (e.g dpdk in guest).=20 It should be ok. Thanks > >> We need more inputs from vendors here. >> >> Thanks >