Subject: Re: PC164 memory bus speeed (was: pciide performance on alpha)
To: None <firstname.lastname@example.org>
From: Simon Burge <email@example.com>
Date: 11/03/1999 00:26:37
Thor Lancelot Simon wrote:
> Okay, so this is an *old* thread. Sorry 'bout that.
Cool, nothing like an old thread to strech the memory :)
> However: you should consider the high cost of incorrectly estimating the
> cache and main memory latencies in the compiler. I suspect that the reason
> almost *all* code seems to run much faster with gcc -mcpu=21164a isn't just
> the use of BWX instructions but also the use of cache and memory latency
> numbers that are a lot closer to reality for the pc164.
> Since we know how fast the L1, L2, and L3 caches are -- L1 and L2 are the
> same for all 21164, and the speed of the L3 parts should be stamped on
> them -- and the memory's 60ns, it should be possible to feed gcc figures
> that are exactly right, and I'd be curious to see what this does for the
> various memory-sensitive benchmarks people have been disappointed by.
How does one do this? I've tried:
gcc -O3 -mcpu=21164a -Wa,-m21164a -mmemory-latency=L1
gcc -O3 -mcpu=21164a -Wa,-m21164a -mmemory-latency=L2
gcc -O3 -mcpu=21164a -Wa,-m21164a -mmemory-latency=main
gcc -O3 -mcpu=21164a -Wa,-m21164a -mmemory-latency=L1 -fsched-interblock -fsched-spec -fsched-spec-load -fbranch-count-reg
Using builtin specs.
gcc version egcs-2.91.66 19990314 (egcs-1.1.2 release)
and get pretty much the same time for my benchmark (between 26.0 and
26.7 seconds). Here's the top of my table of results - I would have
expected the PC164 to be much higher up the list, perhaps less than
wave gcc -O2 3.11 0.04 DEC EV6/667 Tru64 Unix 4.0F
quatre gcc -O2 5.81 0.06 DEC EV65/600 Tru64 Unix 4.0F
numbat gcc -O2 7.22 0.06 Ultra E3000 4/250
x96a gcc -O2 8.76 0.04 Compaq Deskpro EN PII/450 NetBSD 1.4
simonpc gcc -O2 10.46 0.06 PII/400 NetBSD 1.3I
x96c gcc -O2 11.13 0.11 Compaq Deskpro EP/SB Celeron/400 NetBSD 1.4
axp500 cc -O2 12.13 0.08 DEC 500/333
wincen gcc -O2 15.13 0.13 DEC Prioris 6166MP/2 NetBSD 1.4.1
axposf gcc -O2 15.79 0.16 DEC 4000/710
yallara cc -xO3 16.85 0.11 Ultra 2/2200
fbog gcc -O2 19.66 0.06 Ultra 1/200
nsw120 gcc -O2 22.80 0.10 Ultra 2/2170
davros gcc -O2 25.21 0.18 HP 9000/887
scylla gcc -O2 25.87 0.19 DEC PC164/500 NetBSD 1.4
wraith gcc -O2 26.83 0.50 P5/133 NetBSD 1.3.3
"axp500" and "axposf" were some _OLD_ alphas that DEC put on the 'net
years ago for people to play with. I'm sure I don't know the real model
numbers of some of these machines.
Also, this PC164 does have 8 SIMMs, not 4.