Messages in this thread | | | Date | Wed, 20 Oct 2010 10:55:58 +0800 | From | Li Zefan <> | Subject | Re: [RFC PATCH 1/2] perf_events: add support for per-cpu per-cgroup monitoring (v4) |
| |
02:56, stephane eranian wrote: > On Wed, Oct 13, 2010 at 4:26 AM, Li Zefan <lizf@cn.fujitsu.com> wrote: >> (Sorry for the late reply. I've been keeping busy..) >> >> Stephane Eranian wrote: >>> On Fri, Oct 8, 2010 at 2:46 AM, Li Zefan <lizf@cn.fujitsu.com> wrote: >>>>>>>> +#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? >>>> >>> No, timing has to be shared by events monitoring the same cgroup at >>> the same time. >>> Works like a timestamp. It needs to be centralized for all events >>> attached to the same cgroup. >>> >> I no little about internel perf code, so I don't know if we can store >> this somewhere in perf. The last resort could be store it in struct cgroup. >> >>>>>>> - 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 >>>> >>> Ok, but if you mount perf_event twice, you get the >>> same hierarchy id for it: >>> >>> # mount -t cgroup -operf_event none /cgroup >>> # cat /proc/cgroups >>> #subsys_name hierarchy num_cgroups enabled >>> cpuset 0 1 1 >>> cpu 0 1 1 >>> perf_event 1 1 1 >>> >>> # mount -t cgroup -operf_event none /cgroup2 >>> # cat /proc/cgroups >>> #subsys_name hierarchy num_cgroups enabled >>> cpuset 0 1 1 >>> cpu 0 1 1 >>> perf_event 1 1 1 >>> >>> It does not seem like I can mount the same subsystem >>> twice with difference hierarchies: >>> >>> # umount /cgroup2 >>> # mount -t cgroup -operf_event,cpuset none /cgroup2 >>> mount: none already mounted or /cgroup2 busy >>> # mount -t cgroup none /cgroup2 >>> mount: none already mounted or /cgroup2 busy >>> >>>> They now have different hierarchy id, because they belong >>>> to different cgroup hierarchy. >>>> >>>> So pid + hierarchy_id locates the cgroup. >>>> >>> I cannot do task's pid + cgroup hierarchy_id. It's one or the >>> other. >>> >> I've looked into the patch again, and I see you pass the fd from >> userspace, so you don't need hierarchy_id. >> > True. > >> And to get rid of perf_cgroup subsys, seems you just need to find >> another place to store the time info, somewhere inside perf code >> or in struct cgroup. >> > Something I may have missed since the beginning of our conversation > is why do you think definition perf_cgroup subsys is wrong or useless. > What kind of problem does it introduce. I think it is fine to reject cgroup > mode if the perf cgroup is not mounted. >
Actually I don't have strong option over this perf_cgroup subsys. Anyway, I already have cpuacct subsys.
For the disavantage I mentioned before:
- If one mounted cgroup fs without perf cgroup subsys, he can't monitor it.
This is not a problem if we can bind a subsys to a cgroup hierarchy via remount. Currently we can do this only when the cgroupfs has root cgroup only.
For the case that the cgroupfs has child cgroups, adding a subsys to it should not be difficult, but seems removing is another story..
| |