On Mon, Aug 14, 2017 at 10:32:15AM +0100, Bruce Richardson wrote: > On Sat, Aug 12, 2017 at 02:19:45PM -0400, Neil Horman wrote: > > On Fri, Aug 11, 2017 at 09:29:24PM +0100, Bruce Richardson wrote: > > > On Wed, Aug 09, 2017 at 04:21:32PM -0400, Neil Horman wrote: > > > > Can anyone point out to me when and where the change to require SSE4.2 > > > > was > > > > dicussed? The first I saw of it was when the commit to the release > > > > notes went > > > > in on August 3, and I can find no prior mention of it, save for the > > > > patches that > > > > went in separately in the prior weeks. > > > > > > > > Neil > > > > > > > There was no real widespread discussion of it, if that's what you are > > > looking for. I made the proposal via patch, and it was reviewed and > > > acked by a number of folks, with nobody raising any objections at the > > I had a feeling that was the case, and yes, that does concern me somewhat. > > In > > this particular case I think its ok, because I can't really imagine anyone > > using > > older atom processors, but I think it could become problematic in the > > future If > > that support line moves too far into territory in which theres downstream > > support issues (with things like OVS or other tree-external applications) > > > > > time. Possibly it was a change that should have been more widely > > > publicised ahead of time, but I'm not sure what form that publicization > > > should have taken, since all tech discussion happens on the dev mailing > > > list anyway. > > > Not that I'm planning any similar changes, but for the future, what do > > > you think the process for changes like this should be - and what changes > > > would classify for it? If we have a process problem, let's try and fix > > > it. > > > > > > > I don't rightly know, to be honest. DPDK is a little unique in this > > situation, > > since user libraries are built to just access the lowest common denominator > > of a > > given arch. And in many ways, so is the kernel. I'm open to suggestions, > > but I > > think so some sort of plan would be a good idea. These are just off the > > top of > > my head, and likely have drawbacks, but just to get some conversation > > started: > > > > 1) Use extendend ISA instructions opportunistically > > By this I mean to say, we could implement an alternatives system, > > simmilar to what we have in the kernel, which can do dynamic instruction > > replacement based on a run time test. For example, you can write two > > versions > > of a function, one which impements its method with sse4 and another version > > which does the same thing using core isa instructions). If sse4 is > > available at > > runtime, the sse4 variant is mapped in, else the other version is. > > This is something we sort of talked about before, and while theres been > > general support in its philosophy, its the sort of thing that takes alot of > > work, and it is only used in those cases where you know you can use the > > acceleration. > > > > 2) Limit where you introduce hardware deprecation > > Perhaps hardware deprecation can be announced in the same way ABI > > deprecation is, and then introduced at a later date (I would make an opening > > argument for the next LTS release). Using the LTS release as a deprecation > > point is nice because it lets downstream consumers standardize on a release > > without having to worry about hardware support going away. > > > > Just my $0.02. food for thought > > Neil > > > I think the ABI deprecation policy suggestion is a good one, where if we > want to drop support for some HW that was otherwise supported, we should > announce it at least one release in advance to make sure everyone is > aware of it. >
Ok, I can agree with that. Are we also agreed on limiting hardware deprecation to LTS release points? Neil > /Bruce >
