* 858585 jemmy (jemmy858...@gmail.com) wrote: > On Wed, Apr 11, 2018 at 8:29 PM, Dr. David Alan Gilbert > <dgilb...@redhat.com> wrote: > > * Lidong Chen (jemmy858...@gmail.com) wrote: > >> Current Qemu RDMA communication does not support send and receive > >> data at the same time, so when RDMA live migration with postcopy > >> enabled, the source qemu return path thread get qemu file error. > >> > >> Those patch add the postcopy support for RDMA live migration. > > > > This description is a little misleading; it doesn't really > > do RDMA during the postcopy phase - what it really does is disable > > the RDMA page sending during the postcopy phase, relying on the > > RDMA codes stream emulation to send the page. > > Hi Dave: > I will modify the description in next version patch. > > > > > That's not necessarily a bad fix; you get the nice performance of RDMA > > during the precopy phase, but how bad are you finding the performance > > during the postcopy phase - the RDMA code we have was only really > > designed for sending small commands over the stream? > > I have not finished the performance test. There are three choices for RDMA > migration during the postcopy phase. > > 1. RDMA SEND operation from the source qemu > 2. RDMA Write with Immediate from the source qemu > 3. RDMA READ from the destination qemu > > In theory, RDMA READ from the destination qemu is the best way. > But I think it's better to make choice base on the performance result. > I will send the performance result later.
An RDMA read certainly sounds like an interesting way for postcopy, since it means the destination would be in control; so it can RDMA into temporaries that it could then atomically place. An interesting thought. > If use another way during the postcopy phase, it will a big change for the > code. > This patch just make postcopy works, and i will send another patch to > improve the performance. Sure; I just wanted to check that, because the existing code wasn't designed for sending pages, that it wasn't really terribly slow. Dave > Thanks. > > > > > Dave > > > >> Lidong Chen (5): > >> migration: create a dedicated connection for rdma return path > >> migration: add the interface to set get_return_path > >> migration: implement the get_return_path for RDMA iochannel > >> migration: fix qemu carsh when RDMA live migration > >> migration: disable RDMA WRITR after postcopy started. > >> > >> migration/qemu-file-channel.c | 12 ++-- > >> migration/qemu-file.c | 13 +++- > >> migration/qemu-file.h | 2 +- > >> migration/rdma.c | 148 > >> ++++++++++++++++++++++++++++++++++++++++-- > >> 4 files changed, 163 insertions(+), 12 deletions(-) > >> > >> -- > >> 1.8.3.1 > >> > > -- > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
