UPDATE Oracle 8.1.7 on pre EV5.6 = arrghhh

From: Alam, Sim <sim.alam_at_education.tas.gov.au>
Date: Thu, 15 Nov 2001 08:26:22 +1100

Here's an update from Dr Tom:

-----Original Message-----
> Jay summed it all up quite nicely:
> "We had similar difficulties and the explanation for why was difficult
> to
> find, but pretty easy to understand. As I understand it, any Alphas
> before
> EV56 did byte-level math in microcode rather than in the actual
> hardware.
> As a result, those operations were dog-slow compared to longer
> operations.
> EV56 moves these operations into the hardware, resulting in much
better
> performance. Oracle decided to 'optimize' 8.1.7 by recoding to use
> these
> byte-level operations.

Actually, Jay is somewhat mistaken. On all Alpha systems, when you get
an "invalid instruction" trap, control vectors from the PAL into the
system's kernel, and the emulation is all done in software. All of the
things that an EV56 or EV6 (or EV7) processor can do with byte or word
access mode instructions, older processors did with code sequences that
are still generated by the compilers UNLESS you tell the compiler that
it should generate optimized code using byte/word access modes. Until
you tell the compiler to do that, it defaults to using only the older
(and supported on ALL Alpha microprocessors) access modes.

Although the PAL (Privileged Architecture Library) could implement the
logic for byte/word mode instructions on older microprocessors, that
would require re-issuing the PAL (which differs between OpenVMS and
UNIX) for EVERY older system, and you can't guarantee that people will
actually update the console firmware image (which contains the PAL) as
they update the system software or install newer applications; so ALL
of the support for the new instructions on older platforms resides in
system software, NOT in firmware. (If it is in firmware for some of
the platforms, then system software won't get involved, and that's OK,
but it MUST be in system software as well, and consequently, no one is
likely to put it into firmware, because that's LOTS more expensive, and
anyway, the firmware is maintained by the hardware groups who want you
to buy newer hardware.)

Tom
Received on Wed Nov 14 2001 - 21:27:38 NZDT

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