linux-kernel - Re: [PATCH][resubmit] x86: enable preemption in delay

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Message-ID: <20080601162517.GH20824@one.firstfloor.org>
Date:	Sun, 1 Jun 2008 18:25:17 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Marin Mitov <mitov@...p.bas.bg>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-rt-users <linux-rt-users@...r.kernel.org>, akpm@...l.org,
	Ingo Molnar <mingo@...e.hu>,
	Clark Williams <clark.williams@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi-suse@...stfloor.org>
Subject: Re: [PATCH][resubmit] x86: enable preemption in delay

>  static void delay_tsc(unsigned long loops)
>  {
> -	unsigned long bclock, now;
> +	unsigned prev, prev_1, now;
> +	unsigned left = loops;
> +	unsigned prev_cpu, cpu;
> +
> +	preempt_disable();
> +	rdtscl(prev);


The unsigneds should be probably u64  and the rdtsc rdtscll.
Otherwise this will all overflow for longer waits on a very
fast systems (e.g. a 5Ghz system wraps 32bit in ~1.1 seconds)
Normally such delays shouldn't be that long, but why risk
overflow even in extreme cases?

-Andi
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