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Date: Tue, 5 Mar 2013 09:01:34 +0100
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: arch@freebsd.org, Davide Italiano <davide@FreeBSD.org>,
 Alexander Motin <mav@FreeBSD.org>
Subject: tickless design guidelines
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Hi,
i would like a bit of advice on how to get coarse time estimates
(such as "no need to do anything unless at least X msec have elapsed")
in a tickless kernel.

In the past (and I mean a distant one, i got this habit back in 2.x),
rather than calling get*time(),  i used to look at "ticks" to
see if it had changed, and only fetch the actual time accordingly.

This worked well with HZ=1000 or above, when my required accuracy
a few milliseconds. With tickless kernels, i am not sure anymore
how often ticks gets updated.

I may need to do this tests quite frequently (e.g. up to a million
times per second), so I'd rather have some lightweight function.

Any suggestion ?

thanks
luigi