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

[Hari Bathini]

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