linux-kernel - Re: [perf tool] cgroup support broken on Debian?

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Date:	Wed, 17 Dec 2014 03:29:29 +0100
From:	Stephane Eranian <eranian@...glemail.com>
To:	Zefan Li <lizefan@...wei.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephane Eranian <eranian@...gle.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [perf tool] cgroup support broken on Debian?

On Wed, Dec 17, 2014 at 3:20 AM, Zefan Li <lizefan@...wei.com> wrote:
> On 2014/12/17 1:17, Vince Weaver wrote:
>> On Mon, 15 Dec 2014, Stephane Eranian wrote:
>>> On Mon, Dec 15, 2014 at 11:01 PM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
>>
>>> fs is visible. The cgroup file system type is not there anymore. They are using
>>> tmpfs which is not ideal to detect just cgroup. Looks like now, we have to look
>>> at the mount point which is flaky.
>>
>> The trivial fix is to just always assume things will be under
>>       /sys/fs/cgroup
>> which looks like to be the new official mount point.
>>
>> This will break on older systems though, or systems that mount cgroupfs in
>> multiple locations.
>>
>> Another alternative is to change the interface to require the full
>> cgroupfs pathname as an argument to -G
>>
>
> What's the problem here?
>
> none /sys/fs/cgroup tmpfs rw,relatime,size=4k,mode=755 0 0
> systemd /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,perf_event,name=systemd 0 0
>
> cgroup is mounted in /sys/fs/cgroup/systemd, so you should pass '/' to the -G argument:
>
Is that the only mountpoint possible?
The tool needs to detect a valid mount point to locate the named cgroup.
That's assuming that if I create cgroup foo, then it appears under
//sys/fs/cgroup/systemd/foo

>         sudo perf stat -a -e cycles:u,cycles:u,cycles:u -G / -- sleep 1
>
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