I received a few explanations that were very good but I believe yours was
the most complete and easy to understand. I have passed your explanation on
to others here to read. A superb explanation.
Michael C. Rock
-----Original Message-----
From: slug@lists.nks.net [mailto:slug@lists.nks.net]On Behalf Of Timothy
Sent: Wednesday, May 01, 2002 11:40 AM
To: slug@nks.net
Subject: Re: [SLUG] nice and priority on top
This is one of those explanations about Unix/Linux the ordinary user
dreams of. A, pardon the expression, "nice" clear cut explanation in
ordinary understandable language. Bravo!
Timothy
*********** REPLY SEPARATOR ***********
On 5/1/2002 at 10:41 AM Ian C. Blenke wrote:
>On Wed, 2002-05-01 at 10:05, Mikes work account wrote:
>>
>> Can someone explain the difference between the nice value and the
>priority
>> value on the top program. When I change the nice value to 19 to
reduce
>the
>> impace of a process on system performance then the priority goes up
to
>19 as
>> well. Should I change the priority to a lesser value or should it
do it
>on
>> its own when I up the nice value??
>>
>> Michael C. Rock
>
>This is a function of the scheduler.
>
>The process priority is dynamic and constantly changing.
>The nice value of a process is generally static, although you can
>"renice" a running process as often as you wish.
>
>The lower the priority of a process, the more likely it is to be run.
>
>The nice value is added to the priority of a process to adjust its
>importance. A positive nice value will make a process less important.
A
>negative nice value will make a process more important.
>
>The nice value is just a basis for the priority. The scheduler changes
>the priority of a process while it is running. If a process is
resource
>intensive, its priority will drop in the scheduler (the priority
number
>will grow as it is penalized for using resources) to allow other
>processes with lower priority to run.
>
>Think of the nice value as a "priority baseline". As a process gets
more
>time to run, its priority number will grow to the point where it
exceeds
>the priority of other jobs on the system with lower priorities. Once
the
>lower priority processes have had their chance.
>
>Process priority is based on a number of factors aside from simple
>aging, however. CPU use, memory use, IO wait time, and dozens of other
>factors go in to recomputing the constantly changing priorities of
>processes on your system. This is what the scheduler does. Changing
the
>behavior of the scheduler can change the entire "feel" of your
computer
>(making it more/less interactive, or running long-running compute jobs
>more/less efficiently).
>
>Giving a positive nice value will penalize a process so that it will
>always schedule last after everything else has a chance to run.
>
>Giving a negative nice value will give a process preference over other
>running processes on the system. The more negative the nice value, the
>less likely other jobs will be given a chance to run.
>
>To answer your question though, yes the system should update the
>priority to start at the niceness value you set. In fact, it should
>generally never drop below the nice value - at least with the current
>scheduler, AFAIK.
>
>- Ian C. Blenke <icblenke@nks.net> <ian@blenke.com>
>http://ian.blenke.com
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