From owner-freebsd-current@FreeBSD.ORG  Sun Jul 30 09:07:50 2006
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From: Michal Mertl <mime@traveller.cz>
To: Paul Allen <nospam@ugcs.caltech.edu>
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Date: Sun, 30 Jul 2006 11:07:31 +0200
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Cc: Peter Jeremy <peterjeremy@optushome.com.au>, freebsd-current@freebsd.org,
	Brian Candler <B.Candler@pobox.com>
Subject: Re: vmstat's entries type
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Paul Allen wrote:
> >From Michal Mertl <mime@traveller.cz>, Sun, Jul 30, 2006 at 01:50:36AM +0200:
> > Michal Mertl wrote:
> > > Paul Allen wrote:
> > > > Surely all you need to do is a cheap crit_enter,crit_exit 
> > > > while updating the 64-bit per cpu counters.  and on
> > > > a 64-bit arch you skip the crit_enter,crit_exit.
> > > 
> > > Critical_enter/exit seem to be quite lightweight (single
> > > read/modify/write of a variable).
> > 
> > One more question. Why do you say that crit_* can be avoided on 64-bit
> > arch? If the reason was that "increment of a 64 bit number is one
> > operation there" it probably is not true - as somebody already stated,
> > some instruction sets don't allow atomic increment of a memory location.
> > 
> > Michal
> 
> Which FreeBSD tier-I 64b arch do you have in mind...

I was referring to what Peter Jeremy said earlier in this thread:

> RISC architectures usually only have TAS lock primitives (because "inc
> mem" doesn't exist) and so require a spinlock to perform an atomic
> update.

I don't know anything that low level about any platform but i386.

Michal