Date: Wed, 24 Jan 1996 16:01:07 +0530 From: A JOSEPH KOSHY <koshy@india.hp.com> To: asami@cs.berkeley.edu (Satoshi Asami) Cc: hackers@freebsd.org Subject: Re: Pentium bcopy Message-ID: <199601241031.AA281999468@fakir.india.hp.com> In-Reply-To: Your message of "Wed, 24 Jan 1996 01:19:34 PST." <199601240919.BAA28229@silvia.HIP.Berkeley.EDU>
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>>> sa == Satoshi Asami said: sa> Does anyone know if there are any `gotchas' concerning the use of fp sa> regs in the kernel? Are the FPU registers saved and restored as part of interrupt handling? I'm not sure where to look but /usr/src/sys/i386/i386 doesn't seem to have code to do this. Am I looking at the wrong place? You would need to ensure this if you are using your FP-enabled bcopy from any interrupt routine. Blindly saving all FP registers when 'bcopy' is invoked has its own cost, so you probably need to use the FP registers method only if the amount of data to be copied is large. You may need to experiment and determine the best size to switch from regular bcopy to the FP version. Also you need to be sure that the FP registers are accessible. A machine with a 486SX or a plain 386 cannot use this technique. Indeed on a 387 the technique could even be slower than a rep movsl. Lots of tradeoffs here :). Koshy
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