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To: David Xu <davidxu@freebsd.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Fri, 28 Oct 2005 18:43:10 +0800."
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Date: Fri, 28 Oct 2005 12:50:16 +0200
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Cc: Pertti Kosunen <pertti.kosunen@pp.nic.fi>, current@freebsd.org,
	"Yuriy N. Shkandybin" <jura@networks.ru>
Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 
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In message <436200BE.70604@freebsd.org>, David Xu writes:
>Poul-Henning Kamp wrote:
>> In message <4361FDBE.7000500@freebsd.org>, David Xu writes:
>> 
>> 
>> the correct way to optimize this would be to add a time(2) systemcall
>> which returns the value of the kernel global time_second.
>> 
>
>Can we make a page in kernel address space which is readable my user
>code? put the variable in the page, I know read an integer is atomic-op,
>needn't lock, so syscall is not needed.

We have often talked about doing something like that, but so far nobody
has come up with a (sensible) implementation.

Please thing _very_ carefully about the implications for libc
versioning before hacking up a patch.

-- 
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.