2016-09-01 13:46 GMT+08:00 Li, Liang Z <liang.z.li@xxxxxxxxx>: >> 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 <liang.z.li@xxxxxxxxx>: >> > 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 from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
