linux-kernel - Re: [PATCH v4 0/3] perf: add support for analyzing events for containers

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Message-Id: <1d75e250-62dd-6d5b-2644-a79d208b2875@linux.vnet.ibm.com>
Date:   Wed, 4 Jan 2017 17:15:02 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     ast@...com, peterz@...radead.org,
        lkml <linux-kernel@...r.kernel.org>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, mingo@...hat.com,
        daniel@...earbox.net, rostedt@...dmis.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        ebiederm@...ssion.com, sargun@...gun.me,
        Aravinda Prasad <aravinda@...ux.vnet.ibm.com>,
        brendan.d.gregg@...il.com
Subject: Re: [PATCH v4 0/3] perf: add support for analyzing events for
 containers



On Wednesday 04 January 2017 02:34 PM, Krister Johansen wrote:
> On Tue, Jan 03, 2017 at 04:57:54PM +0530, Hari Bathini wrote:
>> On Thursday 29 December 2016 07:11 AM, Krister Johansen wrote:
>>> On Fri, Dec 16, 2016 at 12:06:55AM +0530, Hari Bathini wrote:
>>>> This patch-set overcomes this limitation by using cgroup identifier as
>>>> container unique identifier. A new PERF_RECORD_NAMESPACES event that
>>>> records namespaces related info is introduced, from which the cgroup
>>>> namespace's device & inode numbers are used as cgroup identifier. This
>>>> is based on the assumption that each container is created with it's own
>>>> cgroup namespace allowing assessment/analysis of multiple containers
>>>> using cgroup identifier.
>>> Why choose cgroups when the kernel dispenses namespace-unique
>>> identifiers. Cgroup membership can be arbitrary.  Moreover, cgroup and
>> Agreed. But doesn't that hold for any other namespace or a combination
>> of namespaces as well?
> I guess that's part of my concern.  There is no container-unique
> identifier on the system, since the notion of containers is a construct
> of higer-level software.  You're depending on the fact that some popular
> container software packages put their processes in separate cgroups.
> Some of the stranger problems I've debugged with containers involve
> abuses of nsenter(1) and shared subtrees.  In cases like that, if you
> filter by cgroup you may miss other interfering processes that are in
> one or more of the namespaces associated with the container, but not its
> cgroup.  It's possible I misunderstood.  Is the cgroup id being used to
> filter events, or just for display purposes?

All namespaces info for all threads is captured in perf.data with
PERF_RECORD_NAMESPACES events, which can be used
for post processing. We used cgroup namespace's id in
patch 3/3 for reporting, which can be improved later..

Thanks
Hari