* Peter Xu (pet...@redhat.com) wrote: > On Tue, Sep 07, 2021 at 12:06:15PM +0100, Dr. David Alan Gilbert wrote: > > > > What if we do the 'flush()' before we start post-copy, instead of after > > > > each > > > > iteration? would that be enough? > > > > > > Possibly, yes. This really need David G's input since he understands > > > the code in way more detail than me. > > > > Hmm I'm not entirely sure why we have the sync after each iteration; > > We don't have that yet, do we?
I think multifd does; I think it calls multifd_send_sync_main sometimes, which I *think* corresponds to iterations. Dave > > the case I can think of is if we're doing async sending, we could have > > two versions of the same page in flight (one from each iteration) - > > you'd want those to get there in the right order. > > From MSG_ZEROCOPY document: > > For protocols that acknowledge data in-order, like TCP, each > notification can be squashed into the previous one, so that no more > than one notification is outstanding at any one point. > > Ordered delivery is the common case, but not guaranteed. Notifications > may arrive out of order on retransmission and socket teardown. > > So no matter whether we have a flush() per iteration before, it seems we may > want one when zero copy enabled? > > Thanks, > > -- > Peter Xu > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
