* Zachary Amsden <zamsden@xxxxxxxxxx> wrote: > On 03/18/2010 11:15 AM, Ingo Molnar wrote: > >* Zachary Amsden<zamsden@xxxxxxxxxx> wrote: > > > >>On 03/18/2010 12:50 AM, Ingo Molnar wrote: > >>>* Avi Kivity<avi@xxxxxxxxxx> wrote: > >>> > >>>>>The moment any change (be it as trivial as fixing a GUI detail or as > >>>>>complex as a new feature) involves two or more packages, development speed > >>>>>slows down to a crawl - while the complexity of the change might be very > >>>>>low! > >>>>Why is that? > >>>It's very simple: because the contribution latencies and overhead compound, > >>>almost inevitably. > >>> > >>>If you ever tried to implement a combo GCC+glibc+kernel feature you'll know > >>>... > >>> > >>>Even with the best-run projects in existence it takes forever and is very > >>>painful - and here i talk about first hand experience over many years. > >>Ingo, what you miss is that this is not a bad thing. Fact of the > >>matter is, it's not just painful, it downright sucks. > >Our experience is the opposite, and we tried both variants and report about > >our experience with both models honestly. > > > >You only have experience about one variant - the one you advocate. > > > >See the assymetry? > > > >>This is actually a Good Thing (tm). It means you have to get your > >>feature and its interfaces well defined and able to version forwards > >>and backwards independently from each other. And that introduces > >>some complexity and time and testing, but in the end it's what you > >>want. You don't introduce a requirement to have the feature, but > >>take advantage of it if it is there. > >> > >>It may take everyone else a couple years to upgrade the compilers, > >>tools, libraries and kernel, and by that time any bugs introduced by > >>interacting with this feature will have been ironed out and their > >>patterns well known. > >Sorry, but this is pain not true. The 2.4->2.6 kernel cycle debacle has taught > >us that waiting long to 'iron out' the details has the following effects: > > > > - developer pain > > - user pain > > - distro pain > > - disconnect > > - loss of developers, testers and users > > - grave bugs discovered months (years ...) down the line > > - untested features > > - developer exhaustion > > > >It didnt work, trust me - and i've been around long enough to have suffered > >through the whole 2.5.x misery. Some of our worst ABIs come from that cycle as > >well. > > You're talking about a single project and comparing it to my argument about > multiple independent projects. In that case, I see no point in the > discussion. If you want to win the argument by strawman, you are welcome to > do so. The kernel is a very complex project with many ABI issues, so all those arguments apply to it as well. The description you gave: | This is actually a Good Thing (tm). It means you have to get your feature | and its interfaces well defined and able to version forwards and backwards | independently from each other. And that introduces some complexity and | time and testing, but in the end it's what you want. You don't introduce a | requirement to have the feature, but take advantage of it if it is there. matches the kernel too. We have many such situations. (Furthermore, the tools/perf/ situation, which relates to ABIs and user-space/kernel-space interactions is similar as well.) Do you still think i'm making a straw-man argument? > > Sorry, but i really think you are really trying to rationalize a > > disadvantage here ... > > This could very well be true, but until someone comes forward with > compelling numbers (as in, developers committed to working on the project, > number of patches and total amount of code contribution), there is no point > in having an argument, there really isn't anything to discuss other than > opinion. My opinion is you need a really strong justification to have a > successful fork and I don't see that justification. I can give you rough numbers for tools/perf - if that counts for you. For the first four months of its existence, when it was a separate project, i had a single external contributor IIRC. The moment it went into the kernel repo the number of contributors and contributions skyrocketed and basically all contributions were top-notch. We are at 60+ separate contributors now (after about 8 months upstream) - which is still small compared to the kernel or to Qemu, but huge for a relatively isolated project like instrumentation. So in my estimation tools/kvm/ would certainly be popular. Whether it would be more popular than current Qemu is hard to tell - it would be pure speculation. Any reliable numbers for the other aspect, whether a split project creates a more fragile and less developed ABI would be extremely hard to get. I believe it to be true, but that's my opinion based on my experience with other projects, extrapolated to KVM/Qemu. Anyway, the issue is moot as there's clear opposition to the unification idea. Too bad - there was heavy initial opposition to the arch/x86 unification as well [and heavy opposition to tools/perf/ as well], still both worked out extremely well :-) Ingo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
