Date: Thu, 9 Nov 1995 12:35:24 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: phk@critter.tfs.com (Poul-Henning Kamp) Cc: hasty@rah.star-gate.com, koshy@blr.novell.com, freebsd-hackers@freebsd.org Subject: Re: Load/Store using FPU regs ... Message-ID: <199511091135.MAA08283@labinfo.iet.unipi.it> In-Reply-To: <6539.815911372@critter.tfs.com> from "Poul-Henning Kamp" at Nov 9, 95 11:02:33 am
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> > > > Not to mention that you might not have a FPU. > > > > > > So what ? You still have the FPU emulator :) > > > > Just ignore Pohl's comment we can probably figure out a clever way > > to find out if we have a FPU . > sure, there's a flag in the kernel, and it's a sysctl var too. I was just kidding, but the discussion has become serious! One question: what is the behaviour of our FP library if there is not a coprocessor: do we just trap into the emulator, or the code is magically replaced (e.g. at the first execution) with a call to the proper code ? Anyways using the same technique here seems expensive: the code should look like if (kern.have.fpu) { ... fragment of code using FP regs } else { ... fragment of code using standard techniques } and I don't believe something like this can be done easily by the compiler in a machine-independent way. > The place to use it would be in the Copy-On-Write and Demand-Zero > parts of the VM system. If the scope is limited to such cases, then the kernel could include appropriate code. Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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