linux-kernel - Re: [PATCH v2 1/2] perf: add container identifier entry in perf sample data

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Message-Id: <58edcf4e-80d4-3b0e-773d-29d28070392d@linux.vnet.ibm.com>
Date:   Fri, 2 Sep 2016 19:25:31 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     ast@...com, 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 v2 1/2] perf: add container identifier entry in perf
 sample data



On Thursday 01 September 2016 02:39 PM, Peter Zijlstra wrote:
> On Tue, Aug 30, 2016 at 09:57:02PM +0530, Hari Bathini wrote:
>> Currently, there is no mechanism to filter events based on containers.
>> perf -G can be used, but it will not filter events for the containers
>> created after perf is invoked, making it difficult to assess/analyze
>> performance issues of multiple containers at once. This limitation can
>> be overcome, if there is a standard kernel identifier for containers.
>>
>> This patch introduces a container identifier entry field in perf sample
>> data to identify or distinguish sample data of different containers. It
>> uses the cgroup namespace inode number of a given task as it's container
>> identifier (cid). Alternatively, inode number of pid namespace can also
>> be used as cid. This patch assumes each container is created with it's
>> own cgroup namespace.

Hi Peter,

> I'm thinking this value is mostly the same for tasks, just like COMM and

I think so, too. Namespaces aren't changed that often for tasks...

> MMAP. Could we therefore not emit (sideband) events whenever a task
> changes namespace and get the same information but with tons less data?

You mean, something like PERF_RECORD_NAMESPACE that
emits events on fork, clone, setns..?
  

> That also gives the possibility of recording all namespaces, not just
> the one.

True. If we record all namespaces, container identifier interpretation
can be left to the userspace to decide, which is much more flexible...

Thanks
Hari