Date: Wed, 24 May 2000 22:54:19 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Chuck Paterson <cp@bsdi.com> Cc: Terry Lambert <tlambert@primenet.com>, arch@freebsd.org Subject: Re: Preemptive kernel on older X86 hardware Message-ID: <200005250554.WAA79002@apollo.backplane.com> References: <200005250401.WAA17540@berserker.bsdi.com>
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: : :} Function call overhead is around 17 nS (On a PIII 450) in :} the cache case. :} :} A locked instruction of any sort, non-contending, eats :} 73 nS. : :This means that you use 17ns and on a UP machine with and non locked :cmpxchg the time is going to propably more than double. I :still content that this is the single most important thing :to make fast in the uncontended case and everybit counts. : :Actually this can be decided by experimentation when the :thing is running. It's not like a fundamental design decision. No, such small numbers aren't that important. Do you want me to tell you what the cost of an L2 cache miss is with a *normal* memory read? You might be surprised how bad it is. -Matt Matthew Dillon <dillon@backplane.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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