Help with measuring sleep delay

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Topic: Help with measuring sleep delay.
Url: http://groups.google.com/group/beagleboard/t/e50e431a1d62d418

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From: Jens <jens.g.smeds@gmail.com>
Date: Oct 21 03:36AM -0700
Url: http://groups.google.com/group/beagleboard/msg/49963e19d150e4a2

I started looking at the Linux ACPI code, but I have not really got a
clear view of what causes the variation. I came across a "sys_sync();"
call, which sounds like something that could cause this. The only
thing I've been able to find out about this function is that it "syncs
the file systems".

Since syncing the file system involves writing all outstanding data to the storage device (on a conventional computer to the hard drive or usb stick, but for the beagle most likely to your sd card), could the different time be due to how much data is sitting in cache waiting to be written to the sd card?
Brett.