From owner-freebsd-arch  Wed Jan  2 12:33:32 2002
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Date: Wed, 2 Jan 2002 12:33:23 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: Michal Mertl <mime@traveller.cz>
Cc: Bruce Evans <bde@zeta.org.au>, Mike Smith <msmith@FreeBSD.ORG>,
	Bernd Walter <ticso@cicely8.cicely.de>, <arch@FreeBSD.ORG>
Subject: Re: When to use atomic_ functions? (was: 64 bit counters) 
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:
:I don't know how much time will be wasted - my measurements on pII show
:the atomic_ operations aren't that expensive.

    An atomic operation is not that expensive as long as only one cpu
    is touching the cache line.  Try running two user processes writing
    the same cache line on an SMP system and you will see performance
    drop by a factor of 5-10.

    Now, of course, we could lock each interface to a particular cpu.  There
    are advantages to doing that.

						-Matt

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