On Tue, Mar 30, 2021 at 3:33 PM Song Liu <songliubrav...@fb.com> wrote: > > On Mar 29, 2021, at 4:33 AM, Namhyung Kim <namhy...@kernel.org> wrote: > > > > On Mon, Mar 29, 2021 at 2:17 AM Song Liu <songliubrav...@fb.com> wrote: > >>> On Mar 23, 2021, at 9:21 AM, Namhyung Kim <namhy...@kernel.org> wrote: > >>> > >>> As we can run many jobs (in container) on a big machine, we want to > >>> measure each job's performance during the run. To do that, the > >>> perf_event can be associated to a cgroup to measure it only. > >>> > > [...] > > >>> + return 0; > >>> +} > >> > >> Could you please explain why we need this logic in can_attach? > > > > IIUC the ss->attach() is called after a task's cgroup membership > > is changed. But we want to collect the performance numbers for > > the old cgroup just before the change. As the logic merely checks > > the current task's cgroup, it should be done in the can_attach() > > which is called before the cgroup change. > > Thanks for the explanations. > > Overall, I really like the core idea, especially that the overhead on > context switch is bounded (by the depth of cgroup tree).
Thanks! > > Is it possible to make PERF_EVENT_IOC_ATTACH_CGROUP more flexible? > Specifically, if we can have > > PERF_EVENT_IOC_ADD_CGROUP add a cgroup to the list > PERF_EVENT_IOC_EL_CGROUP delete a cgroup from the list > > we can probably share these events among multiple processes, and > these processes don't need to know others' cgroup list. I think > this will be useful for users to build customized monitoring in > its own container. > > Does this make sense? Maybe we can add ADD/DEL interface for more flexible monitoring but I'm not sure which use cases it'll be used actually. For your multi-process sharing case, the original events' file descriptors should be shared first. Also adding and deleting (or just reading) arbitrary cgroups from a container can be a security concern IMHO. So I just focused on the single-process multi-cgroup case which is already used (perf stat --for-each-cgroup) and very important in my company's setup. In this case we have a list of interested cgroups from the beginning so it's more efficient to create a properly sized hash table and all the nodes at once. Thanks, Namhyung
