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>
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