perf tools: Add 'cgroup_id' sort order keyword

This patch introduces a cgroup identifier entry field in perf report to
identify or distinguish data of different cgroups. It uses the device
number and inode number of cgroup namespace, included in perf data with
the new PERF_RECORD_NAMESPACES event, as cgroup identifier.

With the assumption that each container is created with it's own cgroup
namespace,  this allows assessment/analysis of multiple containers at
once.

A simple test for this would be to clone a few processes passing
SIGCHILD & CLONE_NEWCROUP flags to each of them, execute shell and run
different workloads  on each of those contexts,  while running perf
record command with --namespaces option.

Shown below is the output of perf report, sorted with cgroup identifier,
on perf.data generated with the above test scenario, clearly indicating
one context's considerable use of kernel memory in comparison with
others:

	$ perf report -s cgroup_id,sample --stdio
	#
	# Total Lost Samples: 0
	#
	# Samples: 5K of event 'kmem:kmalloc'
	# Event count (approx.): 5965
	#
	# Overhead  cgroup id (dev/inode)       Samples
	# ........  .....................  ............
	#
	    81.27%  3/0xeffffffb                   4848
	    16.24%  3/0xf00000d0                    969
	     1.16%  3/0xf00000ce                     69
	     0.82%  3/0xf00000cf                     49
	     0.50%  0/0x0                            30

While this is a start, there is further scope of improving this. For
example, instead of cgroup namespace's device and inode numbers, dev
and inode numbers of some or all namespaces may be used to distinguish
which processes are running in a given container context.

Also, scripts to map device and inode info to containers sounds
plausible for better tracing of containers.

Signed-off-by: Hari Bathini <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Ananth N Mavinakayanahalli <[email protected]>
Cc: Aravinda Prasad <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sargun Dhillon <[email protected]>
Cc: Steven Rostedt <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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