Re: Accessing monotonic clock from modules

From: Chris Friesen <cfriesen@nortel.com>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Robert Love <rml@novell.com>,
	Mikael Starvik <mikael.starvik@axis.com>,
	linux-kernel@vger.kernel.org
Subject: Re: Accessing monotonic clock from modules
Date: Thu, 02 Jun 2005 07:46:15 -0600	[thread overview]
Message-ID: <429F0DA7.40006@nortel.com> (raw)
In-Reply-To: <1117698978.6458.23.camel@laptopd505.fenrus.org>

Arjan van de Ven wrote:
>>I do thing that this is useful, though--at GUADEC I talked with some
>>folks who really want to get at a good clock source, the same from both
>>the kernel and user-space.
> 
> 
> I'd love to see one (but preferably 2 or 3) users of this so that we can
> figure out what a good interface would look like...

For ourselves we implemented an clock interface for a limited subset of 
architectures that provides a fast timestamp in kernel and userspace.

Basically it has one call to return a 64-bit timestamp, and another call 
to tell you how fast the clock is ticking.

If it can, it uses things like the x86 cycle counter or the ppc 
timebase.  If there is no arch support, it falls back to clock_gettime.

Chris