On Thu, Apr 19, 2018 at 04:52:20PM +0000, Liang, Cunming wrote: > > > > -----Original Message----- > > From: Paolo Bonzini [mailto:pbonz...@redhat.com] > > Sent: Thursday, April 19, 2018 11:52 PM > > To: Michael S. Tsirkin <m...@redhat.com>; Liang, Cunming > > <cunming.li...@intel.com> > > Cc: Bie, Tiwei <tiwei....@intel.com>; jasow...@redhat.com; > > alex.william...@redhat.com; stefa...@redhat.com; qemu-devel@nongnu.org; > > virtio-...@lists.oasis-open.org; Daly, Dan <dan.d...@intel.com>; Tan, > > Jianfeng > > <jianfeng....@intel.com>; Wang, Zhihong <zhihong.w...@intel.com>; Wang, > > Xiao W <xiao.w.w...@intel.com> > > Subject: Re: [PATCH v3 6/6] vhost-user: support registering external host > > notifiers > > > > On 19/04/2018 17:42, Michael S. Tsirkin wrote: > > >> A compiler barrier is enough on strongly-ordered memory platform. > > >> As it doesn't re-order store, PCI device won't see a stale index > > >> value. But a weakly-ordered memory needs sfence. > > > > > > Oh you are right. > > > > > > So it's only needed for non-intel platforms or when packets are in WC > > > memory then. And I don't know whether dpdk ever puts packets in WC > > > memory. > > > > > > I guess we'll cross this bridge when we get to it. > > > > Non-TSO architectures seem important... > > I'm not familiar with Non-TSO, trying to understand the difference > according to the feature set. Let's say non-TSO architectures do not > set 'weak_barriers'. Then mandatory barrier is used for software. HW > offload on that platform would choose different feature set against > software?
Right. We'll need a flag for this feature for starters. It doesn't exist :) Paolo also points out that we should then add code to disallow migration between setups with and without the feature. > If it's not, essentially we're worried about live migration from a TSO to a > non-TSO architectures platform? Probably not. > > > > Paolo
