On Thu, Jul 27, 2023 at 08:05:44PM +0800, Hao Jia wrote: > > > On 2023/7/19 Hao Jia wrote: > > > > > > On 2023/7/19 Tejun Heo wrote: > > > On Tue, Jul 18, 2023 at 06:08:50PM +0800, Hao Jia wrote: > > > > https://github.com/jiaozhouxiaojia/cgv2-stat-percpu_test/tree/main > > > > > > So, we run `stress -c 1` for 1 second in the asdf/test0 cgroup and > > > asdf/cpu.stat correctly reports the cumulative usage. After removing > > > asdf/test0 cgroup, asdf's usage_usec is still there. What's missing here? > > > > Sorry, some of my expressions may have misled you. > > > > Yes, cpu.stat will display the cumulative **global** cpu time of the > > cgroup and its descendants (the corresponding kernel variable is > > "cgrp->bstat"), and it will not be lost when the child cgroup is > > removed. > > > > Similarly, we need a **per-cpu** variable to record the accumulated > > per-cpu time of cgroup and its descendants. > > The existing kernel variable "cgroup_rstat_cpu(cgrp, cpu)->bstat" is not > > satisfied, it only records the per-cpu time of cgroup itself, > > So I try to add "cgroup_rstat_cpu(cgrp, cpu)->cumul_bstat" to record > > per-cpu time of cgroup and its descendants. > > > > In order to verify the correctness of my patch, I wrote a kernel module > > to compare the results of calculating the per-cpu time of cgroup and its > > descendants in two ways: > > Method 1. Traverse and add the per-cpu rstatc->bstat of cgroup and > > each of its descendants. > > Method 2. Directly read "cgroup_rstat_cpu(cgrp, cpu)->cumul_bstat" in > > the kernel. > > > > When the child cgroup is not removed, the results calculated by the two > > methods should be equal. > > > > > What are you adding? > > I want to add a **per-cpu variable** to record the cumulative per-cpu > > time of cgroup and its descendants, which is similar to the variable > > "cgrp->bstat", but it is a per-cpu variable. > > It is very useful and convenient for calculating the usage of cgroup on > > each cpu, and its behavior is similar to the "cpuacct.usage*" interface > > of cgroup v1. > > > > Hello Tejun, > > I don't know if I explained it clearly, and do you understand what I mean? > > Would you mind adding a variable like this to facilitate per-cpu usage > calculations and migration from cgroup v1 to cgroup v2? Oh yeah, I do. I'm just thinking whether we also want to expose that in the cgroupfs. We are currently not showing anything per-cpu and the output formatting gets nasty with a huge number of CPUs, so maybe that's not going to work out all that well. Anyways, I'll get back to you next week. Thanks. -- tejun
