linux-kernel - Re: [patch] CFS scheduler, -v8

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Message-ID: <20070506085201.GA5860@elte.hu>
Date:	Sun, 6 May 2007 10:52:01 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Esben Nielsen <nielsen.esben@...glemail.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>,
	Zach Carter <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>
Subject: Re: [patch] CFS scheduler, -v8


* Willy Tarreau <w@....eu> wrote:

> Just a hint: while your code here is correct, it is a good practise to 
> check against < 0 instead, so that if for any reason you sometimes 
> forget to cast to signed, the compiler will emit a warning stating 
> that the condition is always false. This would simply become :
> 
> -		if (key < entry->fair_key) {
> +		if ((s64)(key - entry->fair_key) < 0) {

done :-) (Btw., the key is still s64 so the cast is technically 
unnecessary - but now the code would be correct with the key being u64 
too.)

	Ingo

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -60,7 +60,7 @@ static inline void __enqueue_task_fair(s
 		 * We dont care about collisions. Nodes with
 		 * the same key stay together.
 		 */
-		if (key < entry->fair_key) {
+		if ((s64)(key - entry->fair_key) < 0) {
 			link = &parent->rb_left;
 		} else {
 			link = &parent->rb_right;
-
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