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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 26 Feb 2020 12:50:20 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01QCoJEs54263864 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 26 Feb 2020 12:50:19 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B46614C050; Wed, 26 Feb 2020 12:50:19 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8706E4C04A; Wed, 26 Feb 2020 12:50:19 +0000 (GMT) Received: from oc2783563651 (unknown [9.152.224.149]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 26 Feb 2020 12:50:19 +0000 (GMT) Date: Wed, 26 Feb 2020 13:50:18 +0100 From: Halil Pasic To: "Michael S. Tsirkin" Subject: Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM In-Reply-To: <20200226064243-mutt-send-email-mst@kernel.org> References: <20200226094357.25061-1-jasowang@redhat.com> <20200226045128-mutt-send-email-mst@kernel.org> <20200226064243-mutt-send-email-mst@kernel.org> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-TM-AS-GCONF: 00 x-cbid: 20022612-0016-0000-0000-000002EA7143 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20022612-0017-0000-0000-0000334DA0C3 Message-Id: <20200226135018.608185bb.pasic@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-02-26_04:2020-02-26, 2020-02-26 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 malwarescore=0 priorityscore=1501 suspectscore=0 lowpriorityscore=0 mlxscore=0 spamscore=0 adultscore=0 mlxlogscore=843 impostorscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002260096 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by mx0a-001b2d01.pphosted.com id 01QCns4e033671 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 148.163.158.5 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: Jason Wang , qemu-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 26 Feb 2020 06:44:25 -0500 "Michael S. Tsirkin" wrote: > On Wed, Feb 26, 2020 at 06:17:34PM +0800, Jason Wang wrote: > >=20 > > 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 unconditional= ly on > > > > platform without IOMMU support. This can lead unnecessary IOTLB > > > > transactions which will damage the performance. > > > >=20 > > > > Fixing this by check whether the device is backed by IOMMU and di= sable > > > > device IOTLB. > > > >=20 > > > > Reported-by: Halil Pasic > > > > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support") > > > Well it's just an optimization, isn't it? > >=20 > >=20 > > Kind of, or a fix for the performance. > >=20 >=20 > Given this wasn't a regression, it's a valuable enhancement > but Fixes: seems to agressive. IMHO Fixes is appropriate. Telling vhost-net F_ACCESS_PLATFORM when when vdev->dma_as !=3D &address_space_memory results in a severe performance degradation. Regards, Halil [..]