Re: [MLUG] Anyone got a fast modern computer

[Stephen Montgomery-Smith <EMAIL:PROTECTED>]

Stephen Montgomery-Smith wrote:
> Thanks.  Yes it does look like the various threads are working against 
> each other.  I will try to rewrite the program to see if I can mitigate 
> this effect.  Should have a version 1.16 out in a few days.

Well, my early attempts are not working out very well.  So probably 
there will be no version 1.16.  If anyone else wants to try out my 
program, I will still be very grateful.

> 
> It might also be that the very recent linux kernels are very good at 
> handling multithreading.
> 
> On Sat, 5 Jul 2008, Adam Procter wrote:
> 
>> 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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