From owner-freebsd-arch  Wed Jan  2 16: 7:42 2002
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Date: Wed, 2 Jan 2002 18:07:34 -0600
From: Alfred Perlstein <bright@mu.org>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: John Baldwin <jhb@FreeBSD.ORG>, arch@FreeBSD.ORG,
	Bernd Walter <ticso@cicely8.cicely.de>,
	Mike Smith <msmith@FreeBSD.ORG>, Bruce Evans <bde@zeta.org.au>,
	Michal Mertl <mime@traveller.cz>,
	Peter Jeremy <peter.jeremy@alcatel.com.au>
Subject: Re: When to use atomic_ functions? (was: 64 bit counters)
Message-ID: <20020102180734.A82406@elvis.mu.org>
References: <XFMail.020102152920.jhb@FreeBSD.org> <200201030002.g0302Eo60575@apollo.backplane.com>
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In-Reply-To: <200201030002.g0302Eo60575@apollo.backplane.com>; from dillon@apollo.backplane.com on Wed, Jan 02, 2002 at 04:02:14PM -0800
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* Matthew Dillon <dillon@apollo.backplane.com> [020102 18:02] wrote:
> :Look at PCPU_GET/PCPU_SET.  Note that since an interrupt can preempt you and
> :push you off onto another CPU, you have to use a critical section while
> :updating per-CPU variables.  If desired, some kind of free area could be stuck
> :in struct pcpu (or more likely, struct pcpu would hold a pointer to the area)
> :that could be galloc/gfree'd or some such.
> :
> :-- 
> :
> :John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
> :"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/
> 
>     Maybe we are going about this all wrong.  If a particular interface
>     counter can only be modified from the device interrupt, or only be
>     modified while holding the appropriate mutex, do we need any locking
>     at all?

Yes against the collector unless the collector is run periodically
on each cpu to collect the stats.

-- 
-Alfred Perlstein [alfred@freebsd.org]
'Instead of asking why a piece of software is using "1970s technology,"
 start asking why software is ignoring 30 years of accumulated wisdom.'
Tax deductable donations for FreeBSD: http://www.freebsdfoundation.org/

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