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

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Date:	Thu, 18 Dec 2014 11:40:20 +0800
From:	Zefan Li <lizefan@...wei.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	Stephane Eranian <eranian@...il.com>,
	Stephane Eranian <eranian@...glemail.com>,
	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>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [perf tool] cgroup support broken on Debian?

>>>> 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
>>>
>>
>> There can be only one cgroupfs mountpoint which has perf_event subsystem
>> attached to it.
>>
>> So for this setup:
>>
>> mount -t tmpfs /sys/fs/cgroup
>> mkdir /sys/fs/cgroup/memory
>> mkdir /sys/fs/cgroup/perf
>> mount -t cgroup -o memory memcg /sys/fs/cgroup/memory
>> mount -t cgroup -o perf_event perf /sys/fs/cgroup/perf
>>
>> The perf tool will locate the mountpoint as /sys/fs/cgroup/perf.
>>
> You can mount the cgroup fs for perf_event multiple times. I
> tried and it works, though it is useless.
> 

Yes, but they are the same.

> Vince, I think the correct way to detect which entry is for perf_event
> is to look for filesystem type cgroup and option perf_event. It cannot
> be anything else. First match is good enough.
> .

+1

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