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

[Hari Bathini <hbathini@linux.vnet.ibm.com>]

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