Difference in priority

Difference in priority

[Ankit Jain]

hi

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

thanks

ankit

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Re: Difference in priority

[Con Kolivas]

Ankit Jain wrote:
> hi
> 
> 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.

Con

Re: Difference in priority

[Con Kolivas]

Con Kolivas wrote:
> Ankit Jain wrote:
> 
>> hi
>>
>> 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.

That should read dynamic priority-60 in the PRI column.

Cheers,
Con

Re: Difference in priority

[Ankit Jain]

Sorry but iu could not get why are you adding and
subtracting this 60 in priorities. that corelation i
had also got but could not understrand whats this 60?
and also what is this dynamic priority? hows different
from normal priority

thanks

ankit
 --- Con Kolivas <kernel@kolivas.org> wrote: 
> Con Kolivas wrote:
> > Ankit Jain wrote:
> > 
> >> hi
> >>
> >> 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.
> 
> That should read dynamic priority-60 in the PRI
> column.
> 
> Cheers,
> Con
>  

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Re: Difference in priority

[Con Kolivas]

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Ankit Jain wrote:
> Sorry but iu could not get why are you adding and
> subtracting this 60 in priorities. that corelation i
> had also got but could not understrand whats this 60?
> and also what is this dynamic priority? hows different
> from normal priority

Dynamic priority is the current priority the scheduler has allocated to 
a task. It uses it to decide which task to go next; the lower the number 
the better it's priority so it goes first. The subtracting 100 and 60 is 
just what the userspace tools do to represent an obviously complicated 
value.

Please don't top post. It makes it hard to respond appropriately and 
follow email threads.

Cheers,
Con
> 
> thanks
> 
> ankit
>  --- Con Kolivas <kernel@kolivas.org> wrote: 
> 
>>Con Kolivas wrote:
>>
>>>Ankit Jain wrote:
>>>
>>>
>>>>hi
>>>>
>>>>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.
>>
>>That should read dynamic priority-60 in the PRI
>>column.



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Re: Difference in priority

[Lee Revell]

On Wed, 2004-10-13 at 01:08, Randy.Dunlap wrote:
> Lee Revell wrote:
> > On Tue, 2004-10-12 at 21:17, Albert Cahalan wrote:
> > 
> >>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.
> > 
> > 
> > Linux will probably have priority inheritance soon.  See the "Real Time
> > Kernel" thread.
> 
> Is that opinion based any on this article and Linus's comments in it?
> 
> http://news.com.com/A+new+direction+for+Linux+for+gadgets/2100-7344_3-5406291.html?tag=cd.top
> 

No, but priority inheritance is not the same as making Linux an RTOS.

Lee

Re: Difference in priority

[Randy.Dunlap]

Lee Revell wrote:
> On Tue, 2004-10-12 at 21:17, Albert Cahalan wrote:
> 
>>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.
> 
> 
> Linux will probably have priority inheritance soon.  See the "Real Time
> Kernel" thread.

Is that opinion based any on this article and Linus's comments in it?

http://news.com.com/A+new+direction+for+Linux+for+gadgets/2100-7344_3-5406291.html?tag=cd.top


-- 
~Randy

Re: Difference in priority

[Lee Revell]

On Tue, 2004-10-12 at 21:17, Albert Cahalan wrote:
> 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.

Linux will probably have priority inheritance soon.  See the "Real Time
Kernel" thread.

Lee

Re: Difference in priority

[Con Kolivas]

Albert Cahalan writes:

> 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.

As I said; I don't feel strongly. There was an option to change the range of 
real time priorities in 2.4 which is why I mention it. Let others speak 
cause I care not what you do as long as we understand it. I'm not changing 
the scheduler to suit userspace tools.

Cheers,
Con

Re: Difference in priority

[Albert Cahalan]

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.

Re: Difference in priority

[Con Kolivas]

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.

Cheers,
Con

Re: Difference in priority

[Albert Cahalan]

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 had originally tried to match up with Solaris and
a few other systems, but that's looking hopeless.
I intend to change to something sane, perhaps even
making the PRI of "-o pri" be the same as that of "-l".
Currently I don't even try to document PRI.

It is good to keep the value narrow. I really wish
we didn't have so many RT levels; POSIX only requires
that there be 32. A simple 0..99 value would be great.

Here is what I have in my current code, with the
headers edited so they won't be confusing. Note
that the left two versions ("aaa" and "bbb") are
similar to the traditional SysV "pri", but the new
POSIX and UNIX standard makes them unsuitable for use
as the "PRI" displayed by "ps -l". It is common to
generate the "PRI" of "ps -l" via an "opri" keyword.

$ LD_LIBRARY_PATH=../../proc ../../ps/ps -t pts/8 --sort=-priority -o stat,pri,pri_api,rtprio,pri_bar,priority,pri_baz,opri,pri_foo,ni,cls,sched,comm
STAT aaa bbb RTPRIO ccc ddd eee fff ggg  NI CLS SCH COMMAND
SN     0 -40      -  40  39 139  99  19  19  TS   0 setpriority19
Ss+   23 -17      -  17  16 116  76  -4   0  TS   0 bash
S<    39  -1      -   1   0 100  60 -20 -20  TS   0 setpriority-20
S     41   1      1  -1  -2  98  58 -22   -  RR   2 min_rr
S    139  99     99 -99 -100  0 -40 -120  -  FF   1 max_fifo