On Wed, 05.11.14 16:00, Umut Tezduyar Lindskog (u...@tezduyar.com) wrote: > On Wed, Nov 5, 2014 at 2:05 PM, Lennart Poettering > <lenn...@poettering.net> wrote: > > On Wed, 05.11.14 13:41, Umut Tezduyar Lindskog (u...@tezduyar.com) wrote: > > > >> Hi, > >> > >> What is the reasoning for not joining cpu subsystem with systemd subsystem? > >> > >> There are couple ways you can mirror [1] cpu and systemd subsystems > >> and doing so can result completely different cpu bandwidth for > >> processes. > >> > >> I am wondering why we don't mirror them by default. > > > > Because simply enabling a "cpu" controller for a unit already has > > effects on the processes running it. For example, you don't get RT > > anymore, and the general scheduling is altered to schedule your entire > > group evenly against the all groups on the same level. > > Doesn't it make sense to turn it on by default and let users wanting > RT disable it? Seems like this was the case at some point - > http://www.freedesktop.org/wiki/Software/systemd/MyServiceCantGetRealtime/ > (Very much outdated article, we don't have ControlGroup= anymore)
Yeah, I really need to update that article. Generally we should try hard to keep the tree minimal. Resource control enforcement is not free, and hence it should be opt-in, not opt-out. This is something Tejun pretty explicitly asked us for: he wants the most shallow tree that does what is needed. > > systemd will "mirror" a cgroup in the "cpu" hierarchy as soon as you > > set a property on it that requires the "cpu" or "cpuacct" hierarchy, > > for example CPUAccounting=, CPUShares= or CPUQuota. > > You can turn on mirroring during runtime but as far as I know there is > no way going back without rebooting right? In current versions it should correctly turn mirroring off again when you reset the props to their defaults. Lennart -- Lennart Poettering, Red Hat _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel