Why do you need a 387 to run X11R3?
Clayton Haapala
clay at uci.mn.org
Thu Mar 15 01:28:21 AEST 1990
In article <20301 at nuchat.UUCP> steve at nuchat.UUCP (Steve Nuchia) writes:
>Dynamic linking is about the only good solution, but you still have
>to allow the heavy FP users to compile for specific hardware to
>avoid the two jumps per FLOP overhead. There was a scheme proposed
>in which illegal instructions were compiled into the program and
>replaced at run time with the "right" intruction by the kernel. Don't
>know if that ever went out with a commercial system.
I think XENIX uses a variation of that scheme -- an initial fault on the
first time an FP instruction is attempted, then the kernel "hot patches"
the binary with a transfer to the right emulation code. Next time through
there is no fault, just a call. Has to be faster than a complete context
switch with a fault, I would think.
I heard this rumor when I was working with XENIX 3 for 286 boxes. I know
from empirical evidence that XENIX FPP emulation beats the pants off of
SysV 386 emulation.
Say, anybody try the IIT 3C87? It's a clone of the Intel 80387, supposed to
run 25-30% faster. They also have a 287 replacement. I'm thinking of buying
one in a couple of weeks unless I hear terrible things about its performance
under XENIX/UNIX.
--
Clayton Haapala ...!bungia!uci!clay (clay at uci.uci.com)
Unified Communications Inc. "Every morning I get in the Queue.
3001 Metro Drive - Suite 500 'n get on the Bus that takes me to you."
Bloomington, MN 55425 -- the Who
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