[net.lang.c] Vax VMS C compiler

hammond@petrus.UUCP (04/23/85)

Since no one else has done this, I will.  Someone (the article has expired
on our system) posted an article claiming that compiling the UNIX kernel
and utilities with the VAX VMS C compiler resulted in a system which
was 20% faster than the current unix (I assume 4.2 BSD).

I DON"T BELIEVE THIS!!!!!!  If they could get such a performance improvement
their salespersons should be beating down our doors to try and convince us to
run vaxen with ULTRIX rather than other brands.  Paying for ULTRIX as
opposed to free 4.2 BSD would probably be worthwhile if we got a 20%
improvement.

Possible reasons for the claim not being true: 
1) The code is faster, but the system/commands crash (i.e. overzealous
   optimization introduces new bugs)  That is much more believable in
   C than any other language except assembler.
2) Since our vaxen are often I/O bound, speeding things up by 20% merely
   made 20% more idle cycles, not jobs which completed in 80% of their
   former running time.
3) Some things run 20% faster, but you don't see much difference on an
   average workload.  I can believe a smart compiler could make code which
   ran much faster, particularly for floating point.
4) A combination of all of the above.

I am not saying it isn't possible to optimize C code, just that I don't
believe the claims in the absence of any supporting data (i.e. salespersons
bringing those claims to us.

Rich Hammond	{ allegra | decvax | ucbvax} !bellcore!hammond

guy@sun.uucp (Guy Harris) (04/25/85)

> Someone posted an article claiming that compiling the UNIX kernel
> and utilities with the VAX VMS C compiler resulted in a system which
> was 20% faster than the current unix (I assume 4.2 BSD).
> 
> I DON"T BELIEVE THIS!!!!!!  If they could get such a performance improvement
> their salespersons should be beating down our doors to try and convince us
> to run vaxen with ULTRIX rather than other brands.  Paying for ULTRIX as
> opposed to free 4.2 BSD would probably be worthwhile if we got a 20%
> improvement.
> 
> Possible reasons for the claim not being true: 

Possible reason for the claim being true but irrelevant to the merits of
ULTRIX vs. 4.2BSD:

1) ULTRIX uses the same compiler as vanilla 4.2BSD.  I believe this is the
case.  (Adapting the VAX/VMS C compiler may not be trivial; the VAX/VMS
and UNIX object module formats are quite different, and I don't think the
VAX/VMS compiler punts the object module format question the way most UNIX C
compilers do by generating assembly code).

	Guy Harris