Mail Archives: cygwin/2006/03/21/22:18:39
At 07:00 PM 3/21/2006, you wrote:
>jdeifik wrote:
>>I have a dual xeon 2.4ghz machine with hypertreading enabled.
>>This gives me 4 logical processors.
>>The machine dual boots to windows xp sp2, and linux.
>>I have a highly parallelizable program I wrote, and I tested it
>>running 1 to 8 threads,
>>running with no source changes on windows and linux.
>>Here is the performance on linux using gcc-3.4.3
>>threads
>>1 1436.41user 0.10system 7:16.37elapsed 100%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>2 436.00user 0.02system 3:38.15elapsed 199%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>3 369.15user 0.05system 2:03.48elapsed 298%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>4 359.77user 0.08system 1:42.95elapsed 349%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>6 357.83user 0.09system 1:40.94elapsed 354%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>8 358.79user 0.06system 1:41.80elapsed 352%CPU
>>(0avgtext+0avgdata 0maxresident)k
>>To compute efficiency, take the single thread elapsed time/(#
>>threads * threaded elapsed time)
>>There is virtually perfect scaling. 4 processors scale with an
>>efficiency of about 103%.
>>For 6 and 8 threads, efficiency goes up a small amount.
>>
>>Here is the performance on windows xp using cygwin pthreads and gcc-3.4.4
>>1 434.60user 0.20system 7:16.47elapsed 99%CPU (0avgtext+0avgdata
>>509696maxresident)k
>>2 441.78user 0.24system 3:42.06elapsed 199%CPU
>>(0avgtext+0avgdata 510208maxresident)k
>>3 579.68user 0.15system 3:14.50elapsed 298%CPU
>>(0avgtext+0avgdata 511232maxresident)k
>>4 675.39user 0.15system 2:51.50elapsed 393%CPU
>>(0avgtext+0avgdata 512000maxresident)k
>>6 711.70user 0.18system 3:01.20elapsed 392%CPU
>>(0avgtext+0avgdata 511488maxresident)k
>>8 683.35user 0.21system 2:56.05elapsed 388%CPU
>>(0avgtext+0avgdata 512000maxresident)k
>>Things are fine for 2 threads, scaling with an efficiency of 96%
>>For 3 threads, scaling efficiency is 73%
>>For 4 threads, scaling efficiency is 62%
>>For 6 threads, scaling efficiency is 39%
>>For 8 threads, scaling efficiency is 30%
>
>Windows doesn't have HT aware scheduling, such as recent linux
>schedulers incorporate. Cygwin doesn't attempt to improve on the
>Windows scheduler. I won't ask for relevant details about your
>linux, or how you managed to write a program which doesn't deliver
>close to full performance at 2 threads, as that would take this even
>further Off Topic. However, if you are getting good scaling to 2
>threads, that should enable you to get all the dual processor
>performance you can expect in Windows for practical purposes. You
>might try repeating your tests with HT disabled in BIOS.
My linux is mandrake 10.2, I suspect running kernel 2.6.11-13smp.
My program scales perfectly at 2 threads on linux. It also scales
perfectly at 4 threads on linux.
The problem isn't with my program.
I am not sure why it is important to have a HT aware scheduler for
Windows, when there are 4 or more
threads. I can see with 2 threads you would like to have one per
physical processor.
With 4 or more threads, cygwin phtreads really sucks, 4->62%, 6->39%,
8->30% efficiency.
It seems to me that more and more apps are turning to threading for
performance,
and more and more hardware is available with multi-processor,
multi-core, and multi-threading.
Jeff Deifik
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