linux-kernel - Re: [PATCH] sched: Rationalize sys_sched_rr_get

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Date:	Sat, 13 Oct 2007 11:29:33 +1000
From:	Peter Williams <pwil3058@...pond.net.au>
To:	Jarek Poplawski <jarkao2@...pl>
CC:	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>,
	"Siddha\, Suresh B" <suresh.b.siddha@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Rationalize sys_sched_rr_get_interval()

Jarek Poplawski wrote:
> On 12-10-2007 00:23, Peter Williams wrote:
> ...
>> The reason I was going that route was for modularity (which helps when 
>> adding plugsched patches).  I'll submit a revised patch for consideration.
> ...
> 
> IMHO, it looks like modularity could suck here:
> 
>> +static unsigned int default_timeslice_fair(struct task_struct *p)
>> +{
>> +	return NS_TO_JIFFIES(sysctl_sched_min_granularity);
>> +}
> 
> If it's needed for outside and sched_fair will use something else
> (to avoid double conversion) this could be misleading. Shouldn't
> this be kind of private and return something usable for the class
> mainly?

This is supplying data for a system call not something for internal use 
by the class.  As far as the sched_fair class is concerned this is just 
a (necessary - because it's need by a system call) diversion.

> Why anything else than sched_fair should care about this?

sched_fair doesn't care so if nothing else does why do we even have 
sys_sched_rr_get_interval()?  Is this whole function an anachronism that 
can be expunged?  I'm assuming that the reason it exists is that there 
are user space programs that use this system call.  Am I correct in this 
assumption?  Personally, I can't think of anything it would be useful 
for other than satisfying curiosity.

Peter
-- 
Peter Williams                                   pwil3058@...pond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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