Date: Thu, 09 Nov 1995 03:50:57 -0800 From: "Amancio Hasty Jr." <hasty@rah.star-gate.com> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: phk@critter.tfs.com (Poul-Henning Kamp), koshy@blr.novell.com, freebsd-hackers@freebsd.org Subject: Re: Load/Store using FPU regs ... Message-ID: <199511091150.DAA00351@rah.star-gate.com> In-Reply-To: Your message of "Thu, 09 Nov 1995 12:35:24 %2B0100." <199511091135.MAA08283@labinfo.iet.unipi.it>
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>>> Luigi Rizzo said:
> > > > > 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.
>
Let us not forget about the apps... A while back someone did a performance
study on 386bsd and found out that in a typical scenario whatever that
was the kernel spend a considerable amount of time copying things around
maybe from the user space to the kernel space.
Also, something like X can benefit a lot for cases like image copies,etc...
Well thats the last comment about this got to go back to sound driver
hacking...
Have fun guys,
Amancio
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