linux-kernel - Re: [PATCH 0/1] sched: fix typo in sched-rt-group.txt file

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Message-ID: <49b7c2350905192150n4d6b710er571b8a1bd228198b@mail.gmail.com>
Date:	Wed, 20 May 2009 13:50:52 +0900
From:	GeunSik Lim <leemgs1@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	tglx <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH 0/1] sched: fix typo in sched-rt-group.txt file

2009/5/20 GeunSik Lim <leemgs1@...il.com>:
>
>
> Dear Ingo,
>
>
> I made 2 patch files again about static prioriy levels according to ingo's advice
> and explanation. (Reference: http://marc.info/?t=124211992800003&r=1&w=2 archives. )
>
> Fix static priority related range and chart map(userspace/kernelspace) of ftrace.
>   - about chart map of static priority in  ftrace.txt file
>   - about static priority levels(range) in sched-rt-group.txt file
>
>
> commit d6af702008117ca489a2f5476239d1688a517e98
> Author: GeunSik,Lim <leemgs1@...il.com>
> Date:   Tue May 12 17:20:32 2009 +0900
>
>    sched: fix typo in sched-rt-group.txt file
>
>    Fix typo about static priority's range.
>
>    * Kernel Space priority 0(high) to 99(low)   --> User Space RT priority 99(high) to 1(low)
>    * Kernel Space priority 100(high) to 139(low)--> User Space nice -20(high) to 19(low)
>

Ingo,
I want to  change some descriptions according to below discussion.

before) * Kernel Space priority 0(high) to 99(low)   --> User Space RT
priority 99(high) to 1(low)
after)    *  Kernel Space priority 0(high) to 98(low)   --> User Space
RT priority 99(high) to 1(low)

I want to your advice and opinion about this changes.

If I mistook, Please correct me.

thks.



Steven Rostedt:
  Shouldn't that be:
  Kernel priority: 0(high) to 98(low)    ==> user RT priority 99(high) to 1(low)

GeunSik Lim :
  Thank you for your opinion.  I think about corrected expression for
  quick chart to map between kernel space and user space in ftrace .

Steven Rostedt:
 100 items does not map to 99. Which begs the question, what can have
 internal kernel priority 99?

GeunSik Lim :
  ok.  Below example is about  kernel (static) priority 99 that you said.
  please, refer
  to http://www.kernel.org/doc/man-pages/online/pages/man2/sched_setscheduler.2.html
 webpage.

  For processes scheduled under one of the normal scheduling policies
  (SCHED_OTHER, SCHED_IDLE, SCHED_BATCH), sched_priority is not used in
  scheduling decisions (it must be specified as 0).

int main (int argc, char **argv)
{	int pidnumber, ret;
	struct sched_param p;
	p.sched_priority = 0; <------ Kernel (static) priority.
	if (argc != 2) {
		printf("usage: setbatch <pid>\n");
		exit(-1);
	}
	pidnumber = atol(argv[1]);
         /* 3 = Number of SCHED_BATCH Constant */
	ret = sched_setscheduler(pidnumber, 3, &p);
	if (ret) {
		printf("could not set pid %d to SCHED_BATCH: err %d.\n", pid, ret);
		return -1;
	}
	printf("pid %d is SCHED_BATCH from now on.\n", pid);
	return 0;
}


>
>    Processes scheduled with SCHED_OTHER or SCHED_BATCH must be assigned
>    the static priority 0. Processes scheduled under SCHED_FIFO or SCHED_RR
>    can have a static priority in the range 1 to 99.
>    (reference: $> man 2 sched_setscheduler)
>
>    Signed-off-by: GeunSik Lim <geunsik.lim@...sung.com>
>
> diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt
> index 5ba4d3f..1537146 100644
> --- a/Documentation/scheduler/sched-rt-group.txt
> +++ b/Documentation/scheduler/sched-rt-group.txt
> @@ -169,7 +169,7 @@ get their allocated time.
>
>  Implementing SCHED_EDF might take a while to complete. Priority Inheritance is
>  the biggest challenge as the current linux PI infrastructure is geared towards
> -the limited static priority levels 0-139. With deadline scheduling you need to
> +the limited static priority levels 0-99. With deadline scheduling you need to
>  do deadline inheritance (since priority is inversely proportional to the
>  deadline delta (deadline - now).
>
>
>
>
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>
> GeunSik Lim (ELS - OS Group - S/W Lab - SAIT - SAMSUNG)
> e-Mail  :1) geunsik.lim@...sung.com
>         2) leemgs@...il.com , leemgs1@...il.com
> HomePage: http://intomail.dnip.net/invain/me/
> -----------------------------------------------
>



-- 
Regards,
GeunSik Lim
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