Messages in this thread | | | Date | Thu, 27 Jul 2023 20:05:44 +0800 | Subject | Re: [External] Re: [PATCH] cgroup/rstat: record the cumulative per-cpu time of cgroup and its descendants | From | Hao Jia <> |
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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?
Thanks, Hao
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