Subject: Re: [PATCH] Bad rounding in timeval_to_jiffies [was: Re: Odd Timer
	behavior in 2.6 vs 2.4  (1 extra tick)]
From: Steven Rostedt <rostedt@goodmis.org>
To: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: jdavis@accessline.com, Linus Torvalds <torvalds@osdl.org>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
In-Reply-To: <20050421095109.A25431@flint.arm.linux.org.uk>
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Organization: Kihon Technologies
Date: Thu, 21 Apr 2005 06:51:48 -0400
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On Thu, 2005-04-21 at 09:51 +0100, Russell King wrote:
[...]
> The problem is that when you add a timer, you don't have any idea
> which point you're going to be starting your timer at.
> 
> This is why we always round up to the next jiffy when we convert
> times to jiffies - this ensures that you will get at _least_ the
> timeout you requested, which is in itself a very important
> guarantee.
> 

Thanks, I forgot about the guarantee of "at least" the time requested.
I took this on because I noticed this in a driver I wrote. With the user
passing in a timeval for a periodic condition. I noticed that this would
drift quite a bit. I guess I need to write my own timeval_to_jiffies
conversion so that i remove the added jiffy. For this case, I actually
want a true rounded value to the closest jiffy.

Thanks again,

-- Steve


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