Subject: Re: Difference in priority
From: Albert Cahalan <albert@users.sf.net>
To: Con Kolivas <kernel@kolivas.org>
Cc: Albert Cahalan <albert@users.sourceforge.net>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>,
       ankitjain1580@yahoo.com, mingo@elte.hu, rml@tech9.net
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	 <cone.1097626558.804486.12364.502@pc.kolivas.org>
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Date: 12 Oct 2004 21:17:43 -0400
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On Tue, 2004-10-12 at 20:15, Con Kolivas wrote:
> Albert Cahalan writes:
> 
> > Con Kolivas writes:
> >> Ankit Jain wrote:
> > 
> >>> if somebody knows the difference b/w /PRI of both
> >>> these commands because both give different results
> >>>
> >>> ps -Al
> >>> & top
> >>>
> >>> as per priority rule we can set priority upto 0-99
> >>> but top never shows this high priority
> >>
> >> Priority values 0-99 are real time ones and 100-139 are normal 
> >> scheduling ones. RT scheduling does not change dynamic priority while 
> >> running wheras normal scheduling does (between 100-139). top shows the 
> >> value of the current dynamic priority in the PRI column as the current 
> >> dynamic priority-100. If you have a real time task in top it shows as a 
> >> -ve value. ps -Al seems to show the current dynamic priority+60.
> > 
> > What would you like to see? There are numerous
> > competing ideas of reality. There's also the matter
> > of history and standards. I'd gladly "fix" ps, if
> > people could agree on what "fix" would mean.
> > 
> > Various desirable but conflicting traits include:
> > 
> > a. for normal idle processes, PRI matches NI
> > b. for RT processes, PRI matches RT priority
> > c. for RT processes, PRI is negative of RT priority
> > d. PRI is the unmodified value seen in /proc
> > e. PRI is never negative
> > f. low PRI is low priority (SysV "pri" keyword)
> > g. low PRI is high priority (UNIX "PRI", SysV "opri")
> > h. PRI matches some kernel-internal value
> > i. PRI is in the range -99 to 999 (not too wide)
> 
> I can't say I've ever felt strongly about it. Wish I knew what was the best 
> way. If we change the range of RT priority range by increasing it from 100 
> to say 1000 then any arbitrary value to subtract will be wrong. How about 
> just leaving the absolute dynamic priority value? Then we don't have any 
> negative values confusing it, it isn't affected by increasing the range of 
> RT priorities, and better priority values still are lower in value.

That's not convincing enough to overcome inertia.

I can't see why the RT priority range would be increased.
It's overkill already, especially since Linux doesn't have
priority inheritance. Since POSIX requires 32 levels, that
is the right number. Actually using more than one level
(remember: NO priority inheritance) might not be wise.
If we stuck to 32 levels, RT and non-RT could both fit
within a 2-digit positive number. Also, there'd be fewer
bits for the scheduler to examine.


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