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Sender: Alexander Motin <mavbsd@gmail.com>
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Date: Mon, 17 Dec 2012 21:59:41 +0200
From: Alexander Motin <mav@FreeBSD.org>
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Subject: Re: regarding r242905 ('us' argument to some callout functions) was
 Re: [RFC/RFT] calloutng
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Cc: Davide Italiano <davide@freebsd.org>,
 freebsd-current <freebsd-current@freebsd.org>, freebsd-arch@freebsd.org
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Hi.

 > I wonder why the choice is to use (actually, call) the value
 > "microseconds" rather use a bintime or something scaled and with a
 > well defined resolution.

It was kind of engineering choice. I've chosen microseconds, following 
values used by ACPI to represent CPU sleep states exit latencies.  Now 
that is the only usage for that value.  If CPUs so much reduce wakeup 
latencies to make this scale too coarse, this type will be the smallest 
of our optimization tasks. On the other side, I have some doubts that we 
will be able to reach supported 2048 seconds limit on the integer side. 
Now even completely empty idle system has about 30 interrupts per 
second, that is far from 0.0005. From the other side, I don't know any 
system where CPUs have 2048 seconds wakeup latency.

-- 
Alexander Motin