[RFC][PATCH 10/10] taststats: User space with ptop tool

[Michael Holzheu]

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Taskstats user space

The attached tarball "s390-tools-taskstasts.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 enable steal time calculation for non s390
                        modify l_calc_sttime_old() and replact "#if 0"
                        with "#if 1".
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

             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 3 CPUs:

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

  cd linux-2.6.35
  make -j 5

  # ptop_snap_proc
                                            VVVVV
   pid     user  sys  ste cuser  csys cste  total Elap+ Name
   (#)      (%)  (%)  (%)   (%)   (%)  (%)    (%)  (hm) (str)
   8374   75.48 0.41 1.34  0.00  0.00 0.00  77.24  0:01 loop
   8377   73.97 0.27 1.06  0.00  0.00 0.00  75.31  0:01 loop
   8371   70.61 0.38 1.38  0.00  0.00 0.00  72.38  0:01 loop
   10093   0.17 0.30 0.00 25.90 38.19 0.52  65.07  0:00 make
   10548   0.15 0.12 0.00  1.75  4.21 0.06   6.29  0:00 make
   ...
   V:V:S 220.84 2.84 3.86 28.14 43.71 0.60 300.00  0:16
                                           ^^^^^^

  With the snapshot mechanism the sum of all tasks CPU times (user +  
  system + steal + cuser + csystem + csteal) will be exactly 300.00% CPU
  time with this testcase. Using ptop_snap_proc this works fine on
  s390. Unfortunately on x86 the numbers are not as good as on s390.

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