--- Erik Trulsson <[EMAIL PROTECTED]> wrote:

> On Sat, Dec 22, 2007 at 07:09:47PM -0800, Unga
> wrote:
> > Hi all
> > 
> > $ ps -o pri,ni,rtprio,command -p `pgrep amarok`
> > PRI NI  RTPRIO COMMAND
> > 20  0  normal amarokapp
> > 
> > 1) Are there are 3 priority values per process, or
> > just one?
> 
> There is really only one priority that is used when
> scheduling
> processes.  The other two fields (nice and rtprio)
> modifies how
> the priority is set, but do not directly affect the
> priority.
> 
> The actual priority is handled internally in the
> kernel and cannot
> be modified directly from userland.
> 
> 
> It is always the case that if two (or more)
> processes both want
> to use the CPU at the same time, then it is the one
> with the highest
> priority which gets to use it.
> 
> (The term 'highest priority' can be slightly
> confusing, since it is normally
>  the process with the lowest value in the 'PRI'
> field which has the highest
>  priority.)
> 
> For those processes that has a real time priority
> (rtprio) of 'normal',
> i.e. most normal processes, the priority is adjusted
> dynamically
> depending on how long it has waited for CPU, and how
> much CPU it used the
> last time it ran, etc.  The 'nice' value affects how
> quickly the priority
> is adjusted up or down.  A high nice value means
> that the priority will
> only increase slowly and decrease quickly, while it
> is the other way around
> for processes with a low nice value.
> Note however that even a process with a high nice
> value will get at least a
> little CPU time now and then, even if there are
> processes around that are
> much less nice that want the CPU too.
> 
> 
> For processes with a real time priority of something
> other than 'normal' the
> priority is not adjusted dynamically.
> Processes with rtprio=idle always have lower
> priority than all other
> processes.
> Processes with an actual real time priority set will
> always have higher
> priority than non-real time processes.
> 
> 
> 
> > 
> > 2) How should I read above? Is it Priority=20, ie.
> > NI=0, RTPRIO=normal?
> 
> It is:  Priority=20; Nice=0; Real time
> priority=normal
> 
> 
> > Does it all mean the same thing,
> > like the bytes=1048576 and KB=1024 and MB=1?
> 
> No.
> 
> > 
> > 3) The rtprio(1) says "Priority is an integer
> between
> > 0 and RTP_PRIO_MAX (usually 31).  0 is the highest
> > priority". But when I run following command:
> > 
> > $ ps aux -o pri,ni,rtprio,command
> > 
> > USER     PID %CPU %MEM   VSZ   RSS  TT  STAT
> STARTED  
> >    TIME COMMAND          PRI NI  RTPRIO COMMAND
> > 
> > root      10 99.2  0.0     0     8  ??  RL   
> 7:40PM  
> > 0:00.00 [idle: cpu1]     171  0 idle:25 [idle:
> cpu1]
> > 
> > root      26  0.0  0.0     0     8  ??  WL   
> 7:40PM  
> > 0:00.02 [irq18: envy24ht -80  0  intr:4 [irq18:
> > envy24ht
> > 
> > test  1212  0.0  9.3 58544 48176  ??  S     8:06PM
>  
> > 0:06.15 amarokapp         20  0  normal amarokapp
> > 
> > That is,
> >  PID  PRI  NI  RTPRIO
> >   10  171   0  idle:25
> >   26  -80   0  intr:4
> > 1212   20   0  normal
> > 
> > This shows priority ranges at least from -80 to
> 171
> > contrary to the range mentioned in rtprio(1). Does
> > this means PID=26 has a higher priority than
> PID=1212?
> 
> rtprio(1) does not set the PRI field directly. It
> sets the RTPRIO
> field.  In your example these are 'idle:25' 'intr:4'
> and 'normal'
> indicating that these are run with idle priority,
> interrupt priority,
> and normal priority respectively.  (The 'intr' value
> in the rtprio field
> can probably only be set directly by the kernel for
> interrupt threads, and
> is a bit outside the normal real time priorities.)
> 
> The actual idel/real time priority value set by
> rtprio(1)/idprio(1) is not
> displayed by ps(1), but can be shown by
> rtprio(1)/idprio(1).
> 
> 
> Yes, PID=26 has a much higher priority than
> PID=1212, as it should
> considering that PID=26 is an interrupt thread,
> while PID=1212 is just
> an ordinary, non-real time, process.
> 
> 
> > 
> > 4) Can a PRI=0 be considered Realtime?
> 
> No, not really.  If a process does not have rtprio
> set to something
> other than 'normal' or 'idle' it is not a real time
> process.
> 
> > 
> > 5) What is the meaning of priority=0 in
> > /etc/login.conf? Is it Realtime?
> 
> No, the 'priority' field in /etc/login.conf sets the
> nice value.
> 
> > 
> > 6) What is the value should I set for priority in
> > /etc/login.conf if I want Realtime?
> 
> You can't do that.
> 
> You should also not set any process to a real-time
> priority unless
> you know exactly what you are doing and why you are
> doing it.
> 
> The normal way of setting the relative priorities of
> processes on Unix
> systems is by setting the nice value (and only root
> is allowed to lower the
> nice value.)
> 
> 
Thanks for the detailed explanation.

Following is from /usr/include/sys/priority.h:

/*
 * Priorities range from 0 to 255, but differences of
less then 4 (RQ_PPQ)
 * are insignificant.  Ranges are as follows:
 *
 * Interrupt threads:           0 - 63
 * Top half kernel threads:     64 - 127
 * Realtime user threads:       128 - 159
 * Time sharing user threads:   160 - 223
 * Idle user threads:           224 - 255
 *
 * XXX If/When the specific interrupt thread and top
half thread ranges
 * disappear, a larger range can be used for user
processes.
 */

ps aux -o pri,ni,rtprio,command shows following:

USER     PID %CPU %MEM   VSZ   RSS  TT  STAT STARTED  
   TIME COMMAND          PRI NI  RTPRIO COMMAND

root      12 91.0  0.0     0     8  ??  RL    9:50AM
830:41.81 [idle: cpu0]     171  0 idle:25 [idle: cpu0]

root      13  0.0  0.0     0     8  ??  WL    9:50AM  
3:28.96 [swi4: clock sio -32  0 intr:52 [swi4: clock
sio

root     696  0.0  0.1  3240   764  ??  Is    9:51AM  
0:00.06 /usr/sbin/moused  96  0  normal
/usr/sbin/moused

1. Can I further understand how to interpret above
numbers?
1a) 171  0 idle:25
    What is 171? Has is upgraded to “Time sharing user
threads” range to be executed? What is  idle:25? Is it
its default priority 224+25=249?
 
1b) -32  0 intr:52
    What is -32? What is 52?  Is it its default
priority 52 in the “Interrupt threads” range?

1c) 96  0  normal
    The “normal” is what? Is it priority 160 or 223?


2. What is the value range can be specified for
priority in /etc/login.conf?

Regards
Unga



      
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