Subject: Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)
From: Arjan van de Ven <arjan@infradead.org>
To: David Engraf <engraf.david@netcom-sicherheitstechnik.de>
Cc: linux-kernel@vger.kernel.org, "'Andrew Morton'" <akpm@osdl.org>
In-Reply-To: <000001c5fa57$797051b0$0a016696@EW10>
References: <000001c5fa57$797051b0$0a016696@EW10>
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Date: Tue, 06 Dec 2005 12:35:17 +0100
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On Tue, 2005-12-06 at 12:23 +0100, David Engraf wrote:
> > On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
> > > This patch adds a new systemcall on i386 architectures returning the
> jiffies
> > > value to the application. 
> > > As a kernel developer you can use jiffies but from the user space there
> is
> > > no equivalent function which counts every millisecond like the Win32
> > > GetTickCount.
> 
> > a few comments
> 
> > 1) jiffies are 64 bit not 32
> 
> Jiffies is defined as "unsigned long volatile __jiffy_data jiffies". On i386
> machines unsigned long is 32.

but it's a subvariable of jiffies64 which is 64 bit
> 
> 
> > 2) jiffies are not a constant time, eg HZ is a config option,
> >    exposing that internal counter to userspace sounds wrong, after
> >    all what would it be used for
> 
> Right, HZ is defined as USER_HZ which can be set over the config. On normal
> desktop systems it should be 1000 on other machines it could also be 100 or
> 250. Either we can ignore the setting and the function depends on the
> USER_HZ config, or we have to calculate the right value with USER_HZ. 

but then.. why?


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