linux-kernel - Re: [PATCH] sched: fix divide by zero at {thread_group,task}

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Message-ID: <20120813114820.GA2834@redhat.com>
Date:	Mon, 13 Aug 2012 13:48:21 +0200
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] sched: fix divide by zero at {thread_group,task}_times

On Wed, Aug 08, 2012 at 10:08:20PM +0200, Peter Zijlstra wrote:
> On Wed, 2012-08-08 at 21:50 +0200, Mike Galbraith wrote:
> > 32bit built do_div()
> > and div64_u64() both sucked equally compared to 64bit 
> 
> /me peeks at div64_u64 fallback implementation and sees why, it still
> does a single div, it does some neat fls tricks.
> 
> Ok, no point in avoiding this then.. 
> 
> I did the below little edit, no point in mixing the old and new
> primitives.. those __force things annoy me, but I guess otherwise we'll
> upset sparse.

Yeah, __force is needed for sparse, since we marked cputime_t with 
__nocast (by commit 648616343cdbe904c585a6c12e323d3b3c72e46f, which btw
looks like very nice cleanup at whole).

> Index: linux-2.6/kernel/sched/core.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/core.c
> +++ linux-2.6/kernel/sched/core.c
> @@ -3149,7 +3149,7 @@ static cputime_t scale_utime(cputime_t u
>  	temp *= (__force u64) utime;
>  
>  	if (sizeof(cputime_t) == 4)
> -		do_div(temp, (__force u32) total);
> +		temp = div_u64(temp, (__force u32) total);
>  	else
>  		temp = div64_u64(temp, (__force u64) total);

Is this or will be queued (I do not see it queued anywhere)? Or should
I repost with above change?

Thanks
Stanislaw
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