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

[Hari Bathini]

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