Re: [PATCH 1/2] perf_events: add support for per-cpu per-cgroup monitoring (v5)

[Li Zefan <lizf@cn.fujitsu.com>]

Balbir Singh wrote:
> * lizf@cn.fujitsu.com <lizf@cn.fujitsu.com> [2010-11-26 09:50:24]:
> 
>> 19:28, Peter Zijlstra wrote:
>>> On Thu, 2010-11-18 at 12:40 +0200, Stephane Eranian wrote:
>>>> This kernel patch adds the ability to filter monitoring based on
>>>> container groups (cgroups). This is for use in per-cpu mode only.
>>>>     
>>>> The cgroup to monitor is passed as a file descriptor in the pid
>>>> argument to the syscall. The file descriptor must be opened to 
>>>> the cgroup name in the cgroup filesystem. For instance, if the
>>>> cgroup name is foo and cgroupfs is mounted in /cgroup, then the
>>>> file descriptor is opened to /cgroup/foo. Cgroup mode is
>>>> activated by passing PERF_FLAG_PID_CGROUP in the flags argument
>>>> to the syscall.
>>>>
>>>> For instance to measure in cgroup foo on CPU1 assuming
>>>> cgroupfs is mounted under /cgroup:
>>>>
>>>> struct perf_event_attr attr;
>>>> int cgroup_fd, fd;
>>>>
>>>> cgroup_fd = open("/cgroup/foo", O_RDONLY);
>>>> fd = perf_event_open(&attr, cgroup_fd, 1, -1, PERF_FLAG_PID_CGROUP);
>>>> close(cgroup_fd);
>>>>
>>>> Signed-off-by: Stephane Eranian <eranian@google.com> 
>>> Could you please split this patch:
>>>   - pure code movement
>>>   - time accounting changes
>>>   - event_filter_match() stuff
>>>   - cgroup thing
>>>
>>> From a quick reading it doesn't look bad, but I want an ACK from the
>>> cgroup people -- specifically if they're OK with the filedesc juggling
>>> thing, because I know the sysfs people objected to such tricks.
>>>
>> Long long ago, a feature that used this trick was accepted, and that's
>> cgroup taskstat.
>>
>> You get an fd of a cgroup directory and send it to the kernel via netlink,
>> and then you'll receive some statistics, such as how many tasks are
>> running/interrupted in that cgroup.
>>
> 
> That is right, since cgroups don't have id's there is no easy way to
> identify them, looking them up by name and passing strings seemed an
> overkill. 
> 

More information:

Another feature recently added (eventfd-based notifications) also uses fd
to identify a cgroup.