From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id 8A5306B0038 for ; Thu, 1 Sep 2016 02:01:58 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id 33so52432668lfw.1 for ; Wed, 31 Aug 2016 23:01:58 -0700 (PDT) Received: from mail-wm0-x22c.google.com (mail-wm0-x22c.google.com. [2a00:1450:400c:c09::22c]) by mx.google.com with ESMTPS id w127si8066112wmg.118.2016.08.31.23.01.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Aug 2016 23:01:57 -0700 (PDT) Received: by mail-wm0-x22c.google.com with SMTP id c133so60659610wmd.1 for ; Wed, 31 Aug 2016 23:01:56 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1470638134-24149-1-git-send-email-liang.z.li@intel.com> From: Wanpeng Li Date: Thu, 1 Sep 2016 14:01:56 +0800 Message-ID: Subject: Re: [PATCH v3 kernel 0/7] Extend virtio-balloon for fast (de)inflating & fast live migration Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: "Li, Liang Z" Cc: "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "linux-mm@kvack.org" , "virtio-dev@lists.oasis-open.org" , kvm , "qemu-devel@nongnu.org Developers" , "quintela@redhat.com" , "dgilbert@redhat.com" , "Hansen, Dave" 2016-09-01 13:46 GMT+08:00 Li, Liang Z : >> Subject: Re: [PATCH v3 kernel 0/7] Extend virtio-balloon for fast (de)inflating >> & fast live migration >> >> 2016-08-08 14:35 GMT+08:00 Liang Li : >> > This patch set contains two parts of changes to the virtio-balloon. >> > >> > One is the change for speeding up the inflating & deflating process, >> > the main idea of this optimization is to use bitmap to send the page >> > information to host instead of the PFNs, to reduce the overhead of >> > virtio data transmission, address translation and madvise(). This can >> > help to improve the performance by about 85%. >> > >> > Another change is for speeding up live migration. By skipping process >> > guest's free pages in the first round of data copy, to reduce needless >> > data processing, this can help to save quite a lot of CPU cycles and >> > network bandwidth. We put guest's free page information in bitmap and >> > send it to host with the virt queue of virtio-balloon. For an idle 8GB >> > guest, this can help to shorten the total live migration time from >> > 2Sec to about 500ms in the 10Gbps network environment. >> >> I just read the slides of this feature for recent kvm forum, the cloud >> providers more care about live migration downtime to avoid customers' >> perception than total time, however, this feature will increase downtime >> when acquire the benefit of reducing total time, maybe it will be more >> acceptable if there is no downside for downtime. >> >> Regards, >> Wanpeng Li > > In theory, there is no factor that will increase the downtime. There is no additional operation > and no more data copy during the stop and copy stage. But in the test, the downtime increases > and this can be reproduced. I think the busy network line maybe the reason for this. With this > optimization, a huge amount of data is written to the socket in a shorter time, so some of the write > operation may need to wait. Without this optimization, zero page checking takes more time, > the network is not so busy. > > If the guest is not an idle one, I think the gap of the downtime will not so obvious. Anyway, the http://www.linux-kvm.org/images/c/c3/03x06B-Liang_Li-Real_Time_and_Fast_Live_Migration_Update_for_NFV.pdf The slides show almost the similar percentage for the idle and the non-idle guests, they both increase ~50% downtime. Regards, Wanpeng Li -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org