From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juan Quintela Subject: Re: [PATCH v2 00/41] postcopy live migration Date: Thu, 14 Jun 2012 23:07:06 +0200 Message-ID: <87zk85siv9.fsf@elfo.mitica> References: <4FCCABF0.6080907@us.ibm.com> <87y5nyxg4q.fsf@elfo.mitica> <4FD1D2B1.2080108@redhat.com> Reply-To: quintela@redhat.com Mime-Version: 1.0 Content-Type: text/plain Cc: benoit.hudzia@gmail.com, aarcange@redhat.com, Anthony Liguori , kvm@vger.kernel.org, owasserm@redhat.com, stefanha@gmail.com, t.hirofuchi@aist.go.jp, dlaor@redhat.com, satoshi.itoh@aist.go.jp, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com, yoshikawa.takuya@oss.ntt.co.jp, Isaku Yamahata , pbonzini@redhat.com To: Avi Kivity Return-path: In-Reply-To: <4FD1D2B1.2080108@redhat.com> (Avi Kivity's message of "Fri, 08 Jun 2012 13:23:45 +0300") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org Avi Kivity wrote: > On 06/08/2012 01:16 PM, Juan Quintela wrote: >> Anthony Liguori wrote: >> >> Once told that, we need to measure what is the time of an async page >> fault over the network. If it is too high, post copy just don't work. >> >> And no, I haven't seen any measurement that told us that this is going >> to be fast enough, but there is always hope. > > At 10Gb/sec, the time to transfer one page is 4 microseconds. At > 40Gb/sec this drops to a microsecond, plus the latency. This is on par > with the time to handle a write protection fault that precopy uses. But > this can *only* be achieved with RDMA, otherwise the overhead of > messaging and copying will dominate. > > Note this does not mean we should postpone merging until RDMA support is > ready. However we need to make sure the kernel interface is RDMA friendly. Fully agree here. I always thought that postcopy will work with RDMA or something like that, any other thing would just add too much latency. Later, Juan.