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Wed, 13 Nov 2019 16:14:53 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 2w8g17rks5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 13 Nov 2019 16:14:53 +0000 Received: from abhmp0005.oracle.com (abhmp0005.oracle.com [141.146.116.11]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xADGEpHf001616; Wed, 13 Nov 2019 16:14:51 GMT Received: from [10.152.34.2] (/10.152.34.2) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 13 Nov 2019 08:14:51 -0800 Subject: Re: [RFC v4 PATCH 32/49] multi-process: Use separate MMIO communication channel To: Stefan Hajnoczi References: <20191111162132.GI402228@stefanha-x1.localdomain> From: Jag Raman Organization: Oracle Corporation Message-ID: <4a528246-f414-49af-170b-98306b9a0c96@oracle.com> Date: Wed, 13 Nov 2019 11:14:50 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 MIME-Version: 1.0 In-Reply-To: <20191111162132.GI402228@stefanha-x1.localdomain> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9439 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1910280000 definitions=main-1911130144 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9439 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1910280000 definitions=main-1911130145 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] [fuzzy] X-Received-From: 141.146.126.78 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: elena.ufimtseva@oracle.com, fam@euphon.net, thuth@redhat.com, john.g.johnson@oracle.com, ehabkost@redhat.com, konrad.wilk@oracle.com, liran.alon@oracle.com, rth@twiddle.net, quintela@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, ross.lagerwall@citrix.com, mst@redhat.com, kraxel@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, berrange@redhat.com, mreitz@redhat.com, kanth.ghatraju@oracle.com, dgilbert@redhat.com, marcandre.lureau@gmail.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/11/2019 11:21 AM, Stefan Hajnoczi wrote: > On Thu, Oct 24, 2019 at 05:09:13AM -0400, Jagannathan Raman wrote: >> Using a separate communication channel for MMIO helps >> with improving Performance > > Why? Typical initiation of IO operations involves multiple MMIO accesses per IO operation. In some legacy devices like LSI, the completion of the IO operations is also accomplished by polling on MMIO registers. Therefore, MMIO traffic can be hefty in some cases and contribute to Performance. Having a dedicated channel for MMIO ensures that it doesn't have to compete with other messages to the remote process, especially when there are multiple devices emulated by a single remote process. Thanks! -- Jag >