linux-kernel - Re: [PATCH] Avoid overflows in kernel/time.c

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Message-ID: <20071201003333.GR29463@stusta.de>
Date:	Sat, 1 Dec 2007 01:33:33 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Avoid overflows in kernel/time.c

On Thu, Nov 29, 2007 at 04:19:51PM -0800, H. Peter Anvin wrote:
> When the conversion factor between jiffies and milli- or microseconds
> is not a single multiply or divide, as for the case of HZ == 300, we
> currently do a multiply followed by a divide.  The intervening
> result, however, is subject to overflows, especially since the
> fraction is not simplified (for HZ == 300, we multiply by 300 and
> divide by 1000).
>...
>  kernel/Makefile     |    8 +++
>  kernel/time.c       |   29 +++++++++---
>  kernel/timeconst.bc |  123 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 152 insertions(+), 8 deletions(-)
>  create mode 100644 kernel/timeconst.bc
>...

I have read the hep text, but are the advantages of HZ == 300 really 
visible or was this more theoretical?

In the latter case, we might remove the HZ == 300 choice instead.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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