From owner-freebsd-arch  Sun Feb 17 22:29: 5 2002
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To: Bruce Evans <bde@zeta.org.au>
Cc: Terry Lambert <tlambert2@mindspring.com>,
	Matthew Dillon <dillon@apollo.backplane.com>,
	Julian Elischer <julian@elischer.org>,
	Alfred Perlstein <bright@mu.org>, arch@FreeBSD.ORG, jhb@FreeBSD.ORG,
	peter@wemm.org, jake@locore.ca
Subject: Re: gettimeofday() and crhold()/crfree() (was Re: gettimeofday()andcopyout(). Is copyout() MPSAFE on non-i386 archs? ) 
In-Reply-To: Your message of "Mon, 18 Feb 2002 14:52:51 +1100."
             <20020218144148.F4583-100000@gamplex.bde.org> 
Date: Mon, 18 Feb 2002 07:25:50 +0100
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From: Poul-Henning Kamp <phk@critter.freebsd.dk>
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In message <20020218144148.F4583-100000@gamplex.bde.org>, Bruce Evans writes:

>> I *know* that it is a significant win to flip-flop the
>> timecounter context into a reflected user space page
>> on each and every clock interrupt.
>
>That can't be used to implement gettimeofday().  It can only be used
>to implement the userland equivalants of get_micro[up]time() and
>get_nano[up]time().  I don't like using these even for stamping file
>times in seconds in the kernel (though they have more than enough
>precision for this), since they give times that are incoherent
>relative to other ways of determining the time.

Erhm...

I am going to ask to let this this discussion die out now, nobody
seems to have entirely grasped the idea so I think we shall postpone
it until I have some patches.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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