Date: Fri, 25 Jan 2002 15:59:23 -0700 From: Nate Williams <nate@yogotech.com> To: Daniel Eischen <eischen@pcnet1.pcnet.com> Cc: Nate Williams <nate@yogotech.com>, Terry Lambert <tlambert2@mindspring.com>, Dan Eischen <eischen@vigrid.com>, k Macy <kip_macy@yahoo.com>, Peter Wemm <peter@wemm.org>, Julian Elischer <julian@vicor-nb.com>, arch@FreeBSD.ORG Subject: Re: KSE question Message-ID: <15441.58187.656443.659186@caddis.yogotech.com> In-Reply-To: <Pine.SUN.3.91.1020125174754.4674A-100000@pcnet1.pcnet.com> References: <15441.56832.170618.611705@caddis.yogotech.com> <Pine.SUN.3.91.1020125174754.4674A-100000@pcnet1.pcnet.com>
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> > > > The FPU usage is problematic, but is also resolvable, as a > > > > tools issue. > > > > > > > > Specifically, if an ELF section were generated whenever > > > > the compiler generated FPU code (let's call this section > > > > "flags", for the sake of argument), then the flag "FPU=1" > > > > could be set there. > > > > > > [ ... ] > > > > > > Interesting. I think we only care about FPU state > > > during signal deliver and preemptions though, and in > > > that case, the kernel can just pass us the "FPU used" > > > flag and/or "FPU format" along with the interrupted > > > context. > > > > There's lots of talk about using this 'FPU used' flag, but at least my > > read of things from the long discussion before was that it may not be > > possible to implement this on the x86 architectures we currently > > support. > > > > It sounds like a great idea, *IF* if can be done. > > The kernel knows if the FPU has been used and it also knows > the format (x87 vs SSE/XMM). As long as the FPU context > comes from the kernel, then it can also tell us whether > it is valid and it's format. Right, but this has a huge effect on the userlands threads scheduler, since multiple threads can be active during one time-slice, so the userland scheduler will have no way of knowing which thread used the FPU. (At least, not w/out making a system call, defeating most of the advantages of having userland threads...) Nate To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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