Date: Mon, 15 Apr 2002 16:29:22 -0700
From: Terry Lambert <tlambert2@mindspring.com>
To: Poul-Henning Kamp <phk@freebsd.org>
Cc: arch@freebsd.org
Subject: Re: get{bin,micro,nano}[up]time() - what precision ?
Message-ID: <3CBB6252.6BAA4E90@mindspring.com>
References: <54342.1018890897@critter.freebsd.dk>
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Poul-Henning Kamp wrote: > I'm soliciting input from users of the get*time() family of functions > in the kernel on what the minimal desirable precision is. > > Currently they return a timestamp which is no more than 1/HZ out > of date. For contemporary values of HZ, that seems to be adequate. > > As people increase HZ to above 10000, it starts to cost more to > update timecounters every tick, and the question naturally arises: > what is the target resolution for get*time() functions ? > > Would anybody get in trouble if the precision never got better > than 10msec, even for higher HZ ? > > If so, would 1msec be an acceptable limit ? SPARC had a 4uS resolution in ~1990; it did this by having a hardware clock of very high resolution, and a low update frequency, from which a delta was maintained in software, rather than by having an update requirement for a full timecounter like structure. I used this for a 100uS select(2) timeout for pacing in a game, at one point in time. It's probably worth considering Sun's SunOS 4.1.3 approach for FreeBSD. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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