linux-kernel - Re: [PATCH v3 5/6] sched/fair: Rename scale_load() and scale_load

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Date:	Fri, 29 Apr 2016 04:30:07 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, bsegall@...gle.com,
	pjt@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	lizefan@...wei.com, umgwanakikbuti@...il.com
Subject: Re: [PATCH v3 5/6] sched/fair: Rename scale_load() and
 scale_load_down()

On Thu, Apr 28, 2016 at 11:19:19AM +0200, Peter Zijlstra wrote:
> On Tue, Apr 05, 2016 at 12:12:30PM +0800, Yuyang Du wrote:
> > Rename scale_load() and scale_load_down() to user_to_kernel_load()
> > and kernel_to_user_load() respectively, to allow the names to bear
> > what they are really about.
> 
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -189,7 +189,7 @@ static void __update_inv_weight(struct load_weight *lw)
> >  	if (likely(lw->inv_weight))
> >  		return;
> >  
> > -	w = scale_load_down(lw->weight);
> > +	w = kernel_to_user_load(lw->weight);
> >  
> >  	if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
> >  		lw->inv_weight = 1;
> > @@ -213,7 +213,7 @@ static void __update_inv_weight(struct load_weight *lw)
> >   */
> >  static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
> >  {
> > -	u64 fact = scale_load_down(weight);
> > +	u64 fact = kernel_to_user_load(weight);
> >  	int shift = WMULT_SHIFT;
> >  
> >  	__update_inv_weight(lw);

[snip]
 
> Except these 3 really are not about user/kernel visible fixed point
> ranges _at_all_... :/

But are the above two falling back to user fixed point precision? And
the reason being that we can't efficiently do this multiply/divide
thing with increased fixed point for kernel load.