From owner-freebsd-arch  Sun Feb 17 23:42:40 2002
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Date: Sun, 17 Feb 2002 23:42:18 -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: <20020218182727.C5246-100000@gamplex.bde.org>
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Bruce Evans wrote:
> > .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.

In practice, the number was closer to 8-10% of time
burnt on the extra protection domain crossings.  YMMV,
depending on the hardware you end up using, but 10%
was low hanging fruit, and so worth winning back.

The 25% cost for the 2uS number is probably important
to people running blatantly low end hardware, which is
is why I calculated it from there (well, that, and the
overhead I actually had was not in the set of numbers
presented by other people for use in calculations ;^)).

I guess if we could all afford to have $800 ServerWorks
motherboards sontributing to our COGS for our products,
this would be a better world... 8-) 8-).

-- Terry

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