linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Date:	Tue, 24 Apr 2007 09:04:38 +0200
From:	Rogan Dawes <lists@...es.za.net>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Gene Heskett <gene.heskett@...il.com>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Peter Williams <pwil3058@...pond.net.au>,
	ck list <ck@....kolivas.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Lee Irwin III <wli@...omorphy.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bill Davidsen <davidsen@....com>, Willy Tarreau <w@....eu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

Ingo Molnar wrote:

> static void
> yield_task_fair(struct rq *rq, struct task_struct *p, struct task_struct *p_to)
> {
>         struct rb_node *curr, *next, *first;
>         struct task_struct *p_next;
> 
>         /*
>          * yield-to support: if we are on the same runqueue then
>          * give half of our wait_runtime (if it's positive) to the other task:
>          */
>         if (p_to && p->wait_runtime > 0) {
>                 p->wait_runtime >>= 1;
>                 p_to->wait_runtime += p->wait_runtime;
>         }
> 
> the above is the basic expression of: "charge a positive bank balance". 
> 

[..]

> [note, due to the nanoseconds unit there's no rounding loss to worry 
> about.]

Surely if you divide 5 nanoseconds by 2, you'll get a rounding loss?

> 	Ingo

Rogan
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