[parsec-users] the OpenMP version blackscholes has No speedup when has more than 4 cores

Filippo Sironi filippo.sironi at gmail.com
Tue Oct 15 03:12:21 EDT 2013


With the pthreads version I see much better speedups.
Right now I cannot remove the serial part of the benchmark from the computation; however, if we consider the whole execution of the application what I get are the following numbers:

cores	speedup (over the runtime)
1	1
2	1.71
4	2.87
8	4.29
16	5.75
32	6.77

Filippo

On Oct 15, 2013, at 6:58 AM, George Kurian <georgekurian.086 at gmail.com> wrote:

> I would be interested to see if the pthreads version behaves differently from the OpenMP version. Do you observe the same behavior with the pthreads version? What confuses me is why the performance goes down from 2 to 4 to 8 cores (considering blackscholes is embarrassingly parallel and even with initialization included).
> 
> -George
> 
> 
> On Mon, Oct 14, 2013 at 10:13 PM, Eric Lu <eirc.lew at gmail.com> wrote:
> Yes, the performance means speedup, I run blackscholes with simlarge input not native inputs. 
> 
> I will read the paper you recommended. 
> 
> Thanks!
> 
> Eric
> 
> 
> On Tue, Oct 15, 2013 at 9:58 AM, kishore kumar <kishoreguptaos at gmail.com> wrote:
> What do you mean by poor performance? Is it speedup? I guess that you run blackscholes with native inputs. With large inputs, blackscholes main thread does more work (serial execution -- reading input file, etc.,) compared to the worker threads (parallel execution). Around 95% of the entire execution time, you only see one thread, i.e., main thread. May be you want to read "Thread Reinforcer: Dynamically Determining Number of Threads" paper. 
> 
> Thanks.
> 
> Best,
> Kishore Kumar Pusukuri
> http://www.cs.ucr.edu/~kishore
> 
> 
> On Mon, Oct 14, 2013 at 6:34 PM, Eric Lu <eirc.lew at gmail.com> wrote:
> Hi,
> 
> I run PARSEC2.1 on Intel E7520 machine, the os is centos6.3, the gcc-4.7 compiler. The machine has 32 cores in total, and the results seems blackscholes has too poor performance.
> The data shows as follow:
> 	OpenMP
> proc	blackscholes
> 1	0.998269
> 2	1.80499
> 4	1.763301
> 8	1.550916
> 16	1.542871
> 32	2.508076
> 
> 
> 
> Best Regards!
> 
> 
> Eric
> 
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> 
> -- 
> George Kurian
> 5th year Graduate Student,
> Computer Science and Artificial Intelligence Laboratory (CSAIL),
> Massachusetts Institute of Technology.
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