Date: Thu, 22 May 1997 18:12:07 -0600 From: Brett Glass <brett@lariat.org> To: Jim Shankland <jas@flyingfox.com>, gpalmer@FreeBSD.ORG Cc: HARDWARE@FreeBSD.ORG Subject: Re: isa bus and boca multiport boards Message-ID: <3.0.1.32.19970522181207.0072d920@lariat.org> In-Reply-To: <199705221647.JAA03333@biggusdiskus.flyingfox.com>
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At 09:47 AM 5/22/97 -0700, Jim Shankland wrote: >This "tuned asm" thing is perilously close to an urban myth, anyway. >To the extent there's any "lift" to be gotten from asm at all, it's >from tiny little pieces in performance-critical inner loops, Exactly. The guts of the sio driver ARE some performance-critical inner loops. >especially >if there's a hardware-specific instruction that the compiler won't >generate. I'd have to look at the generated code to see how well I/O is done. But I'd HOPE that the macros do the right thing. >It's one thing to say, "I've just spent 3 weeks of backbreaking labor >tuning the sio driver, and made it X% faster; then I experimented and >found that, by replacing the following N lines of C code with assembler, >I made it Y% faster still"; and another to wave one's hands about >a fast sio driver written in assembler. Given the costs in portability, >maintainability, and effort required for assembler, arguments for its >use must be supported by strong, empirical evidence of benefit. My experience on other OS platforms dictates that there IS a large measure of efficiency to be gained -- on the order of 25% time savings. The improvements are partly from ASM and partly from good algorithms. --Brett
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