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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 BA3FCC4BA0B for ; Wed, 26 Feb 2020 10:19:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8996E20838 for ; Wed, 26 Feb 2020 10:19:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NtK2Fplu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8996E20838 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41884 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6tmW-0001Al-PY for qemu-devel@archiver.kernel.org; Wed, 26 Feb 2020 05:19:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:47485) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6tlT-0000Zw-Kt for qemu-devel@nongnu.org; Wed, 26 Feb 2020 05:18:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j6tlS-0000Tp-GD for qemu-devel@nongnu.org; Wed, 26 Feb 2020 05:18:03 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:52916 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j6tlS-0000TD-Bs for qemu-devel@nongnu.org; Wed, 26 Feb 2020 05:18:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582712281; 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=cz7pXOIkDFC5sGtysBOBc/kSfB3RR1nCZ6xj0o75WtY=; b=NtK2Fplu/7lSqfel41pR6M7Puvga8+uijM5a0dPo22K3CeVnyz9oy/MptdwkWwIv5XxKBA vofdCbLm+FCxUwSf6l3G1HxpeSYasFJuP3+pZ8NvQOFKaSgAdQhRcEQxMCQqpAJ13wL18K GrILdCUxf0gDlb2DpSAimMt3r7oBAk4= 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-269-pXsgcyoENAmVHMxhcpFAsQ-1; Wed, 26 Feb 2020 05:17:58 -0500 X-MC-Unique: pXsgcyoENAmVHMxhcpFAsQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3C7A91005514; Wed, 26 Feb 2020 10:17:57 +0000 (UTC) Received: from [10.72.13.217] (ovpn-13-217.pek2.redhat.com [10.72.13.217]) by smtp.corp.redhat.com (Postfix) with ESMTP id BDE5D60BE1; Wed, 26 Feb 2020 10:17:38 +0000 (UTC) Subject: Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM To: "Michael S. Tsirkin" References: <20200226094357.25061-1-jasowang@redhat.com> <20200226045128-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Wed, 26 Feb 2020 18:17:34 +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: <20200226045128-mutt-send-email-mst@kernel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pasic@linux.ibm.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/2/26 =E4=B8=8B=E5=8D=885:53, Michael S. Tsirkin wrote: > On Wed, Feb 26, 2020 at 05:43:57PM +0800, Jason Wang wrote: >> We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on >> platform without IOMMU support. This can lead unnecessary IOTLB >> transactions which will damage the performance. >> >> Fixing this by check whether the device is backed by IOMMU and disable >> device IOTLB. >> >> Reported-by: Halil Pasic >> Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support") > Well it's just an optimization, isn't it? Kind of, or a fix for the performance. > I don't think it's justified to push this to everyone using > vhost with IOTLB, is it? My understanding is that the function should be equivalent to IOTLB in=20 this case. Since no IOMMU is used and device may only see GPA. Another possible direction is to qemu to update memory table via device=20 IOTLB API, this seems less straightforward. > If you disagree, could you comment a bit on which configurations where te= sted? I just do dirty shortcut to emulate the platform without get_dma_as wth=20 IOMMU_PLATFORM set. Thanks > >> Cc: qemu-stable@nongnu.org >> Signed-off-by: Jason Wang > Halil could you test this pls? Does this help your performance issue? > >> --- >> Changes from V1: >> - do not check acked_features >> - reuse vhost_dev_has_iommu() >> --- >> hw/virtio/vhost.c | 12 +++++++++++- >> 1 file changed, 11 insertions(+), 1 deletion(-) >> >> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >> index 9edfadc81d..9182a00495 100644 >> --- a/hw/virtio/vhost.c >> +++ b/hw/virtio/vhost.c >> @@ -290,7 +290,14 @@ static int vhost_dev_has_iommu(struct vhost_dev *de= v) >> { >> VirtIODevice *vdev =3D dev->vdev; >> =20 >> - return virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); >> + /* >> + * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support >> + * incremental memory mapping API via IOTLB API. For platform that >> + * does not have IOMMU, there's no need to enable this feature >> + * which may cause unnecessary IOTLB miss/update trnasactions. >> + */ >> + return vdev->dma_as !=3D &address_space_memory && >> + virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); >> } >> =20 >> static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr, >> @@ -765,6 +772,9 @@ static int vhost_dev_set_features(struct vhost_dev *= dev, >> if (enable_log) { >> features |=3D 0x1ULL << VHOST_F_LOG_ALL; >> } >> + if (!vhost_dev_has_iommu(dev)) { >> + features &=3D ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM); >> + } >> r =3D dev->vhost_ops->vhost_set_features(dev, features); >> if (r < 0) { >> VHOST_OPS_DEBUG("vhost_set_features failed"); >> --=20 >> 2.19.1