From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: MSEC_TO_JIFFIES is messed up...
Date: Wed, 12 May 2004 22:03:05 +0200
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Cc: Jeff Garzik <jgarzik@pobox.com>, Greg KH <greg@kroah.com>,
	Andrew Morton <akpm@osdl.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Netdev <netdev@oss.sgi.com>
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To: Davide Libenzi <davidel@xmailserver.org>
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* Davide Libenzi <davidel@xmailserver.org> wrote:

> > why is it wrong?
> 
> For HZ == 1000 it's fine, even if it'd better to explicitly make it HZ
> dependent and let the compiler to discard them.

the compiler cannot discard the multiplication and the division from the
following:

	x * 1000 / 1000

due to overflows. But we know that HZ is 1000 in the arch-dependent
param.h, and in sched.c we use the HZ dependent variant:

 #ifndef JIFFIES_TO_MSEC
 # define JIFFIES_TO_MSEC(x) ((x) * 1000 / HZ)
 #endif
 #ifndef MSEC_TO_JIFFIES
 # define MSEC_TO_JIFFIES(x) ((x) * HZ / 1000)
 #endif

	Ingo