[RFC][PATCH v2 7/7] taskstats: Precise process accounting user space

[Michael Holzheu <holzheu@linux.vnet.ibm.com>]

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Taskstats user space

The attached tarball "s390-tools-taskstats.tar.bz2" contains user space code
that exploits the taskstasts-top kernel patches. This is early code and
probably still a lot of work has to be done here. The code should build
and work on all architectures, not only on s390.

libtaskstats user space library
-------------------------------
include/libtaskstats.h  API definition
libtaskstats_nl         API implementation based on libnl 1.1
libtaskstats_proc       Partial API implementation using new /proc/taskstats

libtaskstats snapshot user space library
----------------------------------------
include/libtaskstats_snap.h       API definition
libtaskstats_snap/snap_netlink.c  API implementation based on libtaskstats

Snapshot library test program
-----------------------------
ts_snap_test/ts_snap_test.c   Simple program that uses snapshot library

Precise top user space program (ptop)
-------------------------------------
ptop/dg_libtaskstats.c  Data gatherer using taskstats interface
                        To disable steal time calculation for non s390
                        modify l_calc_sttime_old() and replace "#if 1"
                        with "#if 0".
ptop/sd_core.c          Code for ctime accounting

HOWTO build:
============
1.Install libnl-1.1-5 and libnl-1.1-5-devel
  If this is not possible, you can still build the proc/taskstats based code:
  * Remove libtaskstats_nl from the top level Makefile
  * Remove ptop_old_nl, ptop_new_nl and ptop_snap_nl from the "ptop" Makefile
2.Build s390-tools:
  # tar xfv s390-tools.tar.bz2
  # cd s390-tools
  # make

HOWTO use ptop:
===============
In the ptop sub directory there are built five versions of ptop:

* ptop_old_nl:    ptop using the old TASKSTATS_CMD_ATTR_PID netlink command
                  together with reading procfs to find running tasks
* ptop_new_nl:    ptop using the new TASKSTATS_CMD_ATTR_PIDS netlink command.
                  This tool only shows tasks that consumed CPU time in the
                  last interval.
* ptop_new_proc:  ptop using the new TASKSTATS_CMD_ATTR_PIDS ioctl on
                  /proc/taskstats.
                  This tool only shows tasks that consumed CPU time in the
                  last interval.
* ptop_snap_nl:   ptop using the snapshot library with underlying netlink
                  taskstats library
* ptop_snap_proc: ptop using the snapshot library with underlying taskstats
                  library that uses /proc/taskstats

First results (on s390):
========================

TEST1: System with many sleeping tasks
--------------------------------------

  for ((i=0; i < 1000; i++))
  do
         sleep 1000000 &
  done

  # ptop_new_proc

             VVVV
  pid   user  sys  ste  total  Name
  (#)    (%)  (%)  (%)    (%)  (str)
  541   0.37 2.39 0.10   2.87  top
  3645  2.13 1.12 0.14   3.39  ptop_old_nl
  3591  2.20 0.59 0.12   2.92  ptop_snap_nl
  3694  2.16 0.26 0.10   2.51  ptop_snap_proc
  3792  0.03 0.06 0.00   0.09  ptop_new_nl
  3743  0.03 0.05 0.00   0.07  ptop_new_proc
             ^^^^

The ptop user space code is not optimized for a large amount of tasks,
therefore we should concentrate on the system (sys) time. Update time is
2 seconds for all top programs.

* Old top command:
  Because top has to read about 1000 procfs directories, system time is very
  high (2.39%).

* ptop_new_xxx:
  Because only active tasks are transferred, the CPU consumption is very low
  (0.05-0.06% system time).

* ptop_snap_nl/ptop_old_nl:
  The new netlink TASKSTATS_CMD_ATTR_PIDS command only consumes about 50% of
  the CPU time (0.59%) compared to the usage of multiple TASKSTATS_CMD_ATTR_PID
  commands (ptop_old_nl / 1.12%) and scanning procfs to find out running tasks.

* ptop_snap_proc/ptop_snap_nl:
  Using the proc/taskstats interface (0.26%) consumes much less system time
  than the netlink interface (0.59%).

TEST2: Show snapshot consistency with system that is 100% busy
--------------------------------------------------------------

  System with 2 CPUs:

  for ((i=0; i < $(cat /proc/cpuinfo  | grep "^processor" | wc -l); i++))
  do
       ./loop &
  done
  cd linux-2.6
  make -j 5

  # ptop_snap_proc
  pid     user  sys stea cuser  csys cstea xuser xsys xstea  total Name
  (#)      (%)  (%)  (%)   (%)   (%)   (%)   (%)  (%)   (%)    (%) (str)
  2802   43.22 0.35 0.22  0.00  0.00  0.00  0.00 0.00  0.00  43.79 loop
  2799   35.96 0.33 0.21  0.00  0.00  0.00  0.00 0.00  0.00  36.50 loop
  2811    0.04 0.05 0.00 23.22 12.97  0.19  0.00 0.00  0.00  36.46 make
  2796   35.80 0.32 0.19  0.00  0.00  0.00  0.00 0.00  0.00  36.30 loop
  2987   15.93 2.14 0.07  8.23  3.12  0.06  0.00 0.00  0.00  29.53 make
  3044   11.56 1.72 0.22  0.00  0.00  0.00  0.00 0.00  0.00  13.50 make
  3053    1.92 0.73 0.01  0.00  0.00  0.00  0.00 0.00  0.00   2.65 make
  ....
  V:V:S 144.76 6.24 1.22 31.44 16.09  0.25  0.00 0.00  0.00 200.00
                                                            ^^^^^^

  With the snapshot mechanism the sum of all tasks CPU times will be exactly
  200.00% CPU time with this testcase. The following CPU times are used:
  * user/sys/stea:    Time that has been consumed by task itself
  * cuser/csys/cstea: All time that has been consumed by dead children of
                      process.
  * xuser/xsys/xstea: Time that has been consumed by dead threads of thread
                      group of task

  Note that the CPU times on x86 are not as precise as on s390.



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