From owner-freebsd-arch  Sun Feb 17 23:36: 9 2002
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Date: Mon, 18 Feb 2002 18:35:38 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Terry Lambert <tlambert2@mindspring.com>
Cc: Matthew Dillon <dillon@apollo.backplane.com>,
	Poul-Henning Kamp <phk@critter.freebsd.dk>,
	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? )
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On Sun, 17 Feb 2002, Terry Lambert wrote:

> Bruce Evans wrote:
> > On Sun, 17 Feb 2002, Matthew Dillon wrote:
> >
> > >     Just a note:  The gettimeofday() has an overhead of only 2-3 uS in
> > >     -current.  Squid would have to be doing an aweful lot of transactions
> >
> > And that is only on slow machines and/or under SMP.  On my Athlon1600,
> > it has an overhead of 0.3-0.4 nsec.  I have been benchmarking it for
                          argh,   usec
> > many years and recently had to change the benchmark program to use
> > clock_gettime(2) instead of gettimeofday() when getttimeofday()'s
> > resolution became too small.
>
> .4nsec * 22,000 transactions/sec * 5 timestamps/transaction
> = 440us/sec spent on time stamps.

This is not long :-), but 440 msec is.

> Up that to 2uS and... = 220ms/sec on time stamps = ~1/4 of
> all available time spent on time stamps.

Bruce


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