Messages in this thread | | | Date | Fri, 08 Oct 2010 08:46:29 +0800 | From | Li Zefan <> | Subject | Re: [RFC PATCH 1/2] perf_events: add support for per-cpu per-cgroup monitoring (v4) |
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>>>> +#ifdef CONFIG_CGROUPS >>>> +struct perf_cgroup_time { >>>> + u64 time; >>>> + u64 timestamp; >>>> +}; >>>> + >>>> +struct perf_cgroup { >>>> + struct cgroup_subsys_state css; >>>> + struct perf_cgroup_time *time; >>>> +}; >>> Can we avoid adding this perf cgroup subsystem? It has 2 disavantages: >>> >> Well, I need to maintain some timing information for each cgroup. This has >> to be stored somewhere. >>
Seems you can simply store it in struct perf_event?
>>> - If one mounted cgroup fs without perf cgroup subsys, he can't monitor it. >> That's unfortunately true ;-) >> >>> - If there are several different cgroup mount points, only one can be >>> monitored. >>> >>> To choose which cgroup hierarchy to monitor, hierarchy id can be passed >>> from userspace, which is the 2nd column below: >>> >> Ok, I will investigate this. As long as the hierarchy id is unique AND it can be >> searched, then we can use it. Using /proc is fine with me. >> >>> $ cat /proc/cgroups >>> #subsys_name hierarchy num_cgroups enabled >>> debug 0 1 1 >>> net_cls 0 1 1 >>> > > If I mount all subsystems: > mount -t cgroup none /dev/cgroup > Then, I get: > #subsys_name hierarchy num_cgroups enabled > cpuset 1 1 1 > cpu 1 1 1 > perf_event 1 1 1 > > In other words, the hierarchy id is not unique. > If the perf_event is not mounted, then hierarchy id = 0. >
Yes, it's unique. ;)
You mounted them together, and that's a cgroup hierarchy, so they have the same hierarchy id.
If you mount them seperately:
# mount -t cgroup -o debug xxx /cgroup1 # mount -t cgroup -o net_cls xxx /cgroup2/ # cat /proc/cgroups #subsys_name hierarchy num_cgroups enabled debug 1 1 1 net_cls 2 1 1
They now have different hierarchy id, because they belong to different cgroup hierarchy.
So pid + hierarchy_id locates the cgroup.
> When I compare with my approach, if perf_event is > not mounted, then the file descriptor won't lead to the > css, and therefore you will fail and that is fine because > it means the perf_event subsystem is not instantiated > therefore it cannot be used. > > In my patch, there was a missing check for a NULL > css. I fixed that now, and it works fine. > > As for multiple mount points, it seems like the first > mount determines the restrictions for all mounts. > In other words, if you mount only cpuset, then no > other mount can provide more than cpuset, and vice-versa. > > I have tried mounting cgroupfs in multiple places at the same > time. Whatever directory I used, I got to the right css. > > Am I missing your point here? >
I should use the words "cgroup hierarchies" instead of mount points..
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