Date: Sun, 30 Jul 2006 11:07:31 +0200 From: Michal Mertl <mime@traveller.cz> To: Paul Allen <nospam@ugcs.caltech.edu> Cc: Peter Jeremy <peterjeremy@optushome.com.au>, freebsd-current@freebsd.org, Brian Candler <B.Candler@pobox.com> Subject: Re: vmstat's entries type Message-ID: <1154250451.23616.37.camel@genius.i.cz> In-Reply-To: <20060730005342.GJ12597@groat.ugcs.caltech.edu> References: <200607280928.36573.jhb@freebsd.org> <20060728134701.GA45273@uk.tiscali.com> <20060728210154.GC748@turion.vk2pj.dyndns.org> <1154189612.1565.10.camel@genius.i.cz> <20060729205655.GE748@turion.vk2pj.dyndns.org> <20060729211530.GA50342@uk.tiscali.com> <1154212340.3609.18.camel@genius.i.cz> <20060729230214.GI12597@groat.ugcs.caltech.edu> <1154216319.23616.23.camel@genius.i.cz> <1154217036.23616.28.camel@genius.i.cz> <20060730005342.GJ12597@groat.ugcs.caltech.edu>
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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
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