----- Original Message ----- > From: "Yuanhan Liu" <yuanhan.liu at linux.intel.com> > To: "Michael S. Tsirkin" <mst at redhat.com> > Cc: dev at dpdk.org > Sent: Friday, October 16, 2015 10:37:38 AM > Subject: Re: [dpdk-dev] dpdk/vhost-user and VM migration > > On Wed, Oct 14, 2015 at 12:16:29AM +0300, Michael S. Tsirkin wrote: > > Hello! > > I am currently looking at how using dpdk on host, accessing VM memory > > using the vhost-user interface, interacts with VM migration. > > > > The issue is that any changes made to VM memory need to be tracked so > > that updates can be sent from migration source to destination. > > > > At the moment, there's a proposal of an interface extension to > > vhost-user which adds ability to do this tracking through shared memory. > > dpdk would then be responsible for tracking these updates using atomic > > operations to set bits (per page written) in a memory bitmap. > > > > This only needs to happen during migration, at other times there could > > be a jump to skip this logging. > > > > Is this a reasonable approach? > > Hi Michael, > > As I stated in another email, adding dpdk/vhost-user vm migration > support is my second TODO. However, I barely know anything about > vm migration so far, that I can't tell now. > > I will re-visit this question when I finished my first item and > after some more investigation.
Yuanhan, Live-migration for vhost-user is now available upstream. Do you need some guidance on how to implement it in DPDK? Amnon > > --yliu > > > Would performance degradation during > > migration associated with atomics affect the performance to a level > > where it's no longer useful? Pls note these logs aren't latency > > sensitive, so can be done on a separate core, and can be batched. > > > > > > One alternative I'm considering is extending linux kernel so it can do > > this tracking automatically, by marking pages read-only, detecting a > > pagefault and logging the write, then making the pages writeable. This > > would mean higher worst-case overhead (pagefaults are expensive) but > > lower average one (not extra code after the first fault). Not sure how > > feasible this is yet, this would be harder to implement and it will only > > be apply to newer host kernels. > > > > Any feedback would be appreciated. > > > > -- > > MST >
