From owner-freebsd-performance@FreeBSD.ORG  Wed May 10 00:31:42 2006
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Date: Tue, 09 May 2006 17:31:37 -0700
From: Tim Kientzle <kientzle@freebsd.org>
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To: David Xu <davidxu@freebsd.org>
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Cc: performance@freebsd.org, current@freebsd.org,
	Robert Watson <rwatson@freebsd.org>, Kris Kennaway <kris@obsecurity.org>,
	Greg 'groggy' Lehey <grog@freebsd.org>, freebsd-performance@freebsd.org
Subject: Re: Fine-grained locking for POSIX local sockets (UNIX
	domain	sockets)
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David Xu wrote:
> On Wednesday 10 May 2006 02:23, Kris Kennaway wrote:
> 
>>There are at least several issues here:
>>
>>...This may be general issues like
>>gettimeofday() on Linux vs FreeBSD; clearly there is something *very
>>big* to blame here.  Mysql does do *lots* of such calls ...
> 
> My last recall is that gettimeofday is not a syscall on Linux...

I recall Matt talking about implementing gettimeofday()
without a syscall.  The basic idea is to have the kernel
record some constants in a page that's mapped across
all processes, then libc can just read the time from
a known location.

It might be nice to combine this with some of the
other ideas being tossed around here:
   * On each clock tick, store a base time in
a known location (page mapped read-only, no-execute
across all memory maps)
   * libc can just read the base time (accurate
to the clock rate) from a constant.  Very, very fast.
   * For higher resolution, the kernel could record
TSC and CPU clock speed data (per-CPU? Hmmm...)
and libc could use that to fine-tune the time?

Still some details I need to think through...

Tim