From owner-freebsd-arch Wed May 24 22:54:25 2000 Delivered-To: freebsd-arch@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [216.240.41.2]) by hub.freebsd.org (Postfix) with ESMTP id AD8C737B64C for ; Wed, 24 May 2000 22:54:23 -0700 (PDT) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id WAA79002; Wed, 24 May 2000 22:54:19 -0700 (PDT) (envelope-from dillon) Date: Wed, 24 May 2000 22:54:19 -0700 (PDT) From: Matthew Dillon Message-Id: <200005250554.WAA79002@apollo.backplane.com> To: Chuck Paterson Cc: Terry Lambert , arch@freebsd.org Subject: Re: Preemptive kernel on older X86 hardware References: <200005250401.WAA17540@berserker.bsdi.com> Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG : : :} 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message