On Sun, Jun 30, 2013 at 12:39 PM, Lennart Poettering <lpoetter@xxxxxxxxxx> wrote: > Heya, > > > On 29.06.2013 05:05, Tim Hockin wrote: >> >> Come on, now, Lennart. You put a lot of words in my mouth. > > >>> I for sure am not going to make the PID 1 a client of another daemon. >>> That's >>> just wrong. If you have a daemon that is both conceptually the manager of >>> another service and the client of that other service, then that's bad >>> design >>> and you will easily run into deadlocks and such. Just think about it: if >>> you >>> have some external daemon for managing cgroups, and you need cgroups for >>> running external daemons, how are you going to start the external daemon >>> for >>> managing cgroups? Sure, you can hack around this, make that daemon >>> special, >>> and magic, and stuff -- or you can just not do such nonsense. There's no >>> reason to repeat the fuckup that cgroup became in kernelspace a second >>> time, >>> but this time in userspace, with multiple manager daemons all with >>> different >>> and slightly incompatible definitions what a unit to manage actualy is... >> >> >> I forgot about the tautology of systemd. systemd is monolithic. > > > systemd is certainly not monolithic for almost any definition of that term. > I am not sure where you are taking that from, and I am not sure I want to > discuss on that level. This just sounds like FUD you picked up somewhere and > are repeating carelessly... It does a number of sort-of-related things. Maybe it does them better by doing them together. I can't say, really. We don't use it at work, and I am on Ubuntu elsewhere, for now. >> But that's not my point. It seems pretty easy to make this cgroup >> management (in "native mode") a library that can have either a thin >> veneer of a main() function, while also being usable by systemd. The >> point is to solve all of the problems ONCE. I'm trying to make the >> case that systemd itself should be focusing on features and policies >> and awesome APIs. > > You know, getting this all right isn't easy. If you want to do things > properly, then you need to propagate attribute changes between the units you > manage. You also need something like a scheduler, since a number of > controllers can only be configured under certain external conditions (for > example: the blkio or devices controller use major/minor parameters for > configuring per-device limits. Since major/minor assignments are pretty much > unpredictable these days -- and users probably want to configure things with > friendly and stable /dev/disk/by-id/* symlinks anyway -- this requires us to > wait for devices to show up before we can configure the parameters.) Soo... > you need a graph of units, where you can propagate things, and schedule > things based on some execution/event queue. And the propagation and > scheduling are closely intermingled. I'm really just talking about the most basic low-level substrate of writing to cgroupfs. Again, we don't use udev (yet?) so we don't have these problems. It seems to me that it's possible to formulate a bottom layer that is usable by both systemd and non-systemd systems. But, you know, maybe I am wrong and our internal universe is so much simpler (and behind the times) than the rest of the world that layering can work for us and not you. > Now, that's pretty much exactly what systemd actually *is*. It implements a > graph of units with a scheduler. And if you rip that part out of systemd to > make this an "easy cgroup management library", then you simply turn what > systemd is into a library without leaving anything. Which is just bogus. > > So no, if you say "seems pretty easy to make this cgroup management a > library" then well, I have to disagree with you. > > >>> We want to run fewer, simpler things on our systems, we want to reuse as >> >> >> Fewer and simpler are not compatible, unless you are losing >> functionality. Systemd is fewer, but NOT simpler. > > > Oh, certainly it is. If we'd split up the cgroup fs access into separate > daemon of some kind, then we'd need some kind of IPC for that, and so you > have more daemons and you have some complex IPC between the processes. So > yeah, the systemd approach is certainly both simpler and uses fewer daemons > then your hypothetical one. Well, it SOUNDS like Serge is trying to develop this to demonstrate that a standalone daemon works. That's what I am keen to help with (or else we have to invent ourselves). I am not really afraid of IPC or of "more daemons". I much prefer simple agents doing one thing and interacting with each other in simple ways. But that's me. >>> much of the code as we can. You don't achieve that by running yet another >>> daemon that does worse what systemd can anyway do simpler, easier and >>> better. >> >> >> Considering this is all hypothetical, I find this to be a funny >> debate. My hypothetical idea is better than your hypothetical idea. > > > Well, systemd is pretty real, and the code to do the unified cgroup > management within systemd is pretty complete. systemd is certainly not > hypothetical. Fair enough - I did not realize you had already done all the work that Serge is just starting out on. >>> The least you could grant us is to have a look at the final APIs we will >>> have to offer before you already imply that systemd cannot be a valid >>> implementation of any API people could ever agree on. >> >> >> Whoah, don't get defensive. I said nothing of the sort. The fact of >> the matter is that we do not run systemd, at least in part because of >> the monolithic nature. That's unlikely to change in this timescale. > > > Oh, my. I am not sure what makes you think it is monolithic. It is not a replacement for any one thing. It is a replacement for a handful of things that we are not keen to change all at once. That's all. I have not personally looked at what subsystems are able to be compiled-out so we could do an incremental changeover, though, so maybe it can work in different modes? I don't know. I am not pursuing this anyway, so I am not the person to convince, regardless. >> What I said was that it would be a shame if we had to invent our own >> low-level cgroup daemon just because the "upstream" daemons was too >> tightly coupled with systemd. > > > I have no interest to reimplement systemd as a library, just to make you > happy... I am quite happy with what we already have.... > > >> This is supposed to be collaborative, not combative. > > > It certainly sounds *very* differently in what you are writing. Sorry, then. No offense intended. I'm just looking for opportunities to not-replicate work, if this whole model is going to be thrust upon me. Tim _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
