From owner-freebsd-arch  Sun Feb 17 23:24:40 2002
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Date: Sun, 17 Feb 2002 23:21:47 -0800
From: Terry Lambert <tlambert2@mindspring.com>
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To: Bruce Evans <bde@zeta.org.au>
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? )
References: <20020218151249.E4728-100000@gamplex.bde.org>
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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
> 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.

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


[ ... other stuff not really applicable; can discuss why
      off list, if necessary ... ]

-- Terry

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