Hello, Peter. On Tue, May 19, 2015 at 05:16:59PM +0200, Peter Zijlstra wrote: > .gitconfig: > > [diff "default"] > xfuncname = "^[[:alpha:]$_].*[^:]$" > > Will avoid keying on labels like that and show us this is > __cgroup_procs_write(). Ah, nice trick. > So my only worry with this patch-set is that these operations will be > hugely expensive. > > Now it looks like the cgroup_update_dfl_csses() thing is very rare, its > when you change which controllers are active in a given subtree under > the uber-l337-super-comount design. > > The other one, __cgorup_procs_write() is every /procs, /tasks write to a > cgroup, and that does worry me, this could be a somewhat common thing. > > The Changelog states task migration is a cold path, but is tens of > miliseconds per task really no problem? The latency is bound by synchronize_sched_expedited(). Given the way cgroups are used in majority of setups (process migration happening only during service / session setups), I think this should be okay. I agree that something which is closer to lglock in characteristics would fit the workload better tho. If this actually becomes a problem, we can come up with a different percpu locking scheme which puts a bit more overhead on the reader side to reduce the latency / overhead on the writer side which shouldn't be that difficult but let's see whether we need to get there at all. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
