On Tue, Aug 01, 2017 at 01:17:45PM -0700, Tejun Heo wrote: > > What about the whole double accounting thing? Because currently cpuacct > > and cpu do a fair bit of duplication. It would be very good to get rid > > of that. > > I'm not that sure at this point. Here are my current thoughts on > cpuacct. > > * It is useful to have basic cpu statistics on cgroup without having > to enable the cpu controller, especially because enabling cpu > controller always changes how cpu cycles are distributed and > currently comes at some performance overhead. > > * On cgroup2, there is only one hierarchy. It'd be great to have > basic resource accounting enabled by default on all cgroups. Note > that we couldn't do that on v1 because there could be any number of > hierarchies and the cost would increase with the number of > hierarchies. Yes, the whole single hierarchy thing makes doing away with the double accounting possible. > * It is bothersome that we're walking up the tree each time for > cpuacct although being percpu && just walking up the tree makes it > relatively cheap. So even if its only CPU local accounting, you still have all the pointer chasing and misses, not to mention that a faster O(depth) is still O(depth). > Anyways, I'm thinking about shifting the > aggregation to the reader side so that the hot path always only > updates local counters in a way which can scale even when there are > a lot of (idle) cgroups. Will follow up on this later. Not entirely sure I follow, we currently only update the current cgroup and its immediate parents, no? Or are you looking to only account into the current cgroup and propagate into the parents on reading? -- 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
