Re: [MLUG] Anyone got a fast modern computer

[Adam Procter <EMAIL:PROTECTED>]

Stephen Montgomery-Smith wrote:
> Look at the output of the 3rd program - it spent more time on sys than 
> user!  Probably means that the multiple multithreading creates more work 
> than it saves!  Probably copying cache from one core to another!
>
> And the output of the 4th program - it looks like the computer usage was 
> about 1000%!  That's not bad.  Although the timings aren't great.  Maybe 
> that would run about as well with fewer threads - who knows.
>
>   

Yup, top was showing about 1000% the whole time (usually just slightly 
over).

Just got done running with gcc-4.1.2 and -march=nocona, and the 
improvement was pretty slight. I might be doing something really dumb, 
for all I know -- I don't know much about parallel processing.  :) I'll 
send you records.txt off-list. Let me know if there are any other 
compiler flags you want to try.

I was thinking one good thing to try would be to rig up a script that 
varies NR_THREADS and holds everything else constant, but unfortunately 
there's a hard ulimit of 80 minutes per thread on this machine, so 
reducing the number of threads may put me over that limit. Nevertheless, 
I'll give it a try with ten and eight threads -- the high sys time 
(would copying cache actually be counted there?) almost makes me wonder 
if the extra thread synchronization overhead isn't actually slowing 
things down.

'Course the server itself is a couple years old, so it might be that the 
CPUs are simply not as fast as they might be. Can any hardware gurus 
decipher/comment on the following?

processor       : 15
vendor_id       : GenuineIntel
cpu family      : 15
model           : 4
model name      :                   Intel(R) Xeon(TM) CPU 2.80GHz
stepping        : 8
cpu MHz         : 2793.159
cache size      : 1024 KB
physical id     : 3
siblings        : 4
core id         : 7
cpu cores       : 2
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall 
nx lm pni monitor ds_cpl est cid cx16 xtpr lahf_lm
bogomips        : 5586.19
clflush size    : 64
cache_alignment : 128
address sizes   : 40 bits physical, 48 bits virtual
power management:

(x16, of course)


> By the way, if your machine is really a nocona machine, then 
> -march=native means the same thing.  Nevertheless, I do suspect that in 
> this arena that the more modern compilers really have made dramatic 
> improvements, even if no -march is used.  (For the lurkers, -march 
> specifies the architecture.)
>   

Ahh, I gotcha. I *think* nocona is right for this machine, but I'm not 
completely sure. Anyone know if there's a utility that will figure this 
out automatically without the need to build all of gcc-4.2? Seems the 
best source I can find is this: http://gentoo-wiki.com/Safe_Cflags

Adam

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