[Devel] Re: [PATCH v2 5/5] expose per-taskgroup schedstats in cgroup

[Sha Zhengju]

On Wed, Apr 18, 2012 at 10:44 PM, Sha Zhengju <handai.szj at gmail.com> wrote:
> On Mon, Apr 9, 2012 at 6:25 PM, Glauber Costa <glommer at parallels.com> wrote:
>> This patch aims at exposing stat information per-cgroup, such as:
>>  * idle time,
>>  * iowait time,
>>  * steal time,
>>  * # context switches
>> and friends. The ultimate goal is to be able to present a per-container view of
>> /proc/stat inside a container. With this patch, everything that is needed to do
>> that is in place, except for number of tasks.
>>
>> For most of the data, I achieve that by hooking into the schedstats framework,
>> so although the overhead of that is prone to discussion, I am not adding anything,
>> but reusing what's already there instead. The exception being that the data is
>> now computed and stored in non-task se's as well, instead of entity_is_task() branches.
>> However, I expect this to be minimum comparing to the alternative of adding new
>> hierarchy walks. Those are kept intact.
>>
>> The format of the new file added is the same as the one recently
>> introduced for cpuacct:
>>
>>  cpu0.idle X
>>  cpu0.steal Y
>>  ...
>>  cpu1.idle X1
>>  cpu1.steal Y1
>>  ...
>>
>
> You define the idle time as the sum of task's sleeping time which i
> think it needs to
> discuss. It changes the current meaning of idle time which might be confusing
> and can not reflect the the actual cpu busy-idle situation. IMHO, idle
> time can just
> be the true system value. Personally I prefer to your last version in
> the way of computing
> idle time (http://thread.gmane.org/gmane.linux.kernel/1194838). And
> iowait can be
> computed in the similar way.
>
> As to steal time, "Steal time is the percentage of time a virtual CPU
> waits for a real
> CPU while the hypervisor is servicing another virtual processor".
> Speaking from the
> point of view of resource controlling(isolation), cgroup is a
> lightweight method towards
> virtualiztion, so I think obeying its primitive meaning is more
> appropriate: the time not
> servicing me including time stolen by the tasks of other cgroup.

I have a different version of exposing per-cgroup /proc/stat (parts of
them come from your patchset : )  ). I can sent them out if necessary.


Thanks,
Sha