Message-Id: <200710111458.l9BEwBoo022386@tigris.pounder.sol.net>
To: cygwin AT cygwin DOT com
From: cygzw AT trodman DOT com (Tom Rodman)
Reply-to: cygwin AT cygwin DOT com
Subject: interpretation of %CPU in 'procps' output for multi-cpu & hyperthreading
Date: Thu, 11 Oct 2007 09:58:10 -0500
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Pls look at the example below (PS1 prompt def shown, and shell
alias/funct defs shown). Notice that gzip is listed as having 3
threads ( 'OurServer109' is a 4 CPU box with hyperthreading on, so
it has 8 virtual CPUs ).

I would guess gzip must run on exactly 1 cpu, at any given time.
If so, then at most, gzip could use 1/8 of the total
CPU resources or 12.5%, as reported by windows task manager,
right?  So procps is reporting the percent of the current virtual CPU,
that gzip is using, right?

Notice that 'pslist' (from SysInternals) shows gzip, using
9%; 9/12.5 * 100 = 72% of 1 virtual CPU.

Is there a way to prove that a given process with more than 1 thread,
is still restricted to just one CPU?

Any comments/corrections of my misconceptions, appreciated.

We're running 
'CYGWIN_NT-5.2 OurServer109 1.5.20s(0.155/4/2) 20060403 13:33:45 i686 Cygwin'.

--
thanks,
Tom

--my ugly two line shell prompt:
# 09:18:49 Thu 071011 2j tty3 9692 ~
# OurServer109 staffuser1 $ echo $PS1  #9692 is $$
# \t \D{%a %y%m%d} \jj \l 9692 \w\n# \h \u $
--snip
# 09:04:51 Thu 071011 2j tty3 9692 /adm/bin/sys/s
# OurServer109 staffuser1 $ ps_ -C gzip
  PID  PPID %CPU S    VSZ USER     TT        SESS  PGRP  START COMMAND
 9564  6712 87.4 R   2060 staffuser1  tty0      6712  9564  07:47 gzip OurSrvr063#e_drive#Installs.bkf
# 09:11:50 Thu 071011 2j tty3 9692 /adm/bin/sys/s
# OurServer109 staffuser1
--snip
# 09:12:22 Thu 071011 2j tty3 9692 /adm/bin/sys/s
# OurServer109 staffuser1 $ _top
9:12:33 AM 10/11/2007 Process information for OurServer109:
Name                Pid CPU Thd  Hnd   Priv        CPU Time    Elapsed Time
Idle                  0  89   8    0      0   756:50:46.203    97:50:32.617
gzip               6924   9   3   67   2060     1:14:46.171     1:25:34.382
pslist             6688   1   2   90    960     0:00:00.187     0:00:01.249
cqmghost           3352   1  13  223   3176     1:04:59.343    97:50:13.054
--snip
# 09:18:37 Thu 071011 2j tty3 9692 ~
# OurServer109 staffuser1 $ which ps_
ps_ is aliased to `procps -wwHo pid,ppid,%cpu,state,vsize,user,tty,session,pgrp,bsdstart,args'
# 09:18:43 Thu 071011 2j tty3 9692 ~
# OurServer109 staffuser1 $ which _top
_top is a function
_top ()
{
    pslist -s ${1:-2} | perl -ne '
    next if $. == 1;
      # skip first run, since it usually does not correct CPU% (bug in PsList 1.26)
      # 1st pslist line would match regex on next code line below

    $trig = m{Process information for } if (!$after1streport);
      #regex flips true then never used again

    $after1streport=1 if $trig;

    if ( ($after1streport) and (!$zero_percent_CPU) )
    {
      print "\n" if ($zero_percent_CPU = m{^\w+\s+\d+\s+0\s+});
        #only triggers on 1st process using under 1% CPU

      print unless ($zero_percent_CPU or m{^\s*$});
    }
    else
    { if(m{Process information for }) {$zero_percent_CPU=0;print} }
  '
}


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