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

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Message-ID: <20071201133359.2e609976@the-village.bc.nu>
Date:	Sat, 1 Dec 2007 13:33:59 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Adrian Bunk <bunk@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Avoid overflows in kernel/time.c

On Sat, 1 Dec 2007 13:20:47 +0000
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> On Sat, 1 Dec 2007 01:33:33 +0100
> Adrian Bunk <bunk@...nel.org> wrote:
> 
> > 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?
> 
> Its visibile for people doing PAL media processing and TV sync work.

Wake up Alan - NTSC for 300HZ, PAL is OK at 250HZ setting.

Alan
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