scheduling priority not working?

[Zhang Weiwu]

Erik Trulsson wrote:

>On Sat, Feb 28, 2004 at 11:37:51AM +0800, Zhang Weiwu wrote:
>  
>
>>Hello. I thought scheduling priority is the kind of absolute priority, that 
>>is only when the higher priority process don't ask for resource, can the 
>>lower priority process gets resource. If the higher priority process sucks, 
>>the lower priority process starvs.
>>
>>Now I have a old Pentium-mmx 166 box, running mpg321 fine. I wish to listen 
>>to music when recompile the kernel, so turn on the music, do:
>>#nice make;
>>I thought "nice make" use the resouce mpg321 left to it, but actually the 
>>music process is seriously disturbed, it begins to sound like .... 
>>terrible.
>>
>>So I don't realy understand the scheduling priority mechnism in FreeBSD?
>>    
>>
>
>No, you dont quite understand the scheduling.
>There are actually two different priorities that influence scheduling.
>If you look at the output from top(1) you can see them in the columns
>labeled 'PRI' and 'NICE'.  The first one ('PRI') is the one that is
>actually used to determine when a process gets to run. This is
>dynamically adjusted by the system to make sure that all processes get
>at least *some* CPU-time (so no process can be completely starved.) The
>second ('NICE') is what is changed by the nice/renice commands and
>affects how the actual priority is changed by the system. (Processes
>with a high nice-value essentially gets their priority raised slowly
>and lowered quickly .)
>  
>
I don't understand. I watched top(1) for some time, it seems the mpg321 
process, having NICE=-20, keep constant PRI of 108~110, but other 
processes like 'yacc', 'cc', although running at NICE=4, comes out even 
at PRI=120, and almost keep that high until it finish its work in 
several seconds and quit, meanwhile the speaker keep producing broken 
music. If NICE=-20 processes cannot have more PRI than NICE=4, what's 
the use of NICE?

>I run at a very similar box, but use mpg123 rather than mpg321, and I
>can play music without significant disturbance.
>You might wish to try mpg123 instead, in my experience it needs less
>CPU-power than mpg321.
>  
>
My mpg123 hangs after copyright notice. It's another story though.

>You could also try using a higher nice value for the make process. (i.e
>run it with 'nice -19 make' or something like that.)
>  
>
I tried 'nice -n 19 make' which gives 'badly formed number' error. 'nice 
-19 make' made 'make' even greedy.