[erlang-questions] SMP performance with hackbench

[Sean Cribbs]

In a dual quad-core setup, consider that there will be different 
message-passing speeds between:

1) cores on the same chip
2) cores on different chips
3) in some cases, cores in different combinations on the same chip (e.g. 
Nehalem quad-core processors have paired cores with some shared cache)

If you're crossing boundaries between chips/cores frequently, you have 
to go through a cache or main RAM, which will be slower than running all 
on the same core.  Try increasing the number of processes dramatically 
in your test and see how the SMP vs. non-SMP scenario pans out. 40 
processes could be considered a small number of processes for an Erlang 
application.

Sean Cribbs

Jiang Wei wrote:
> Hi, list
>      I write hackbench in erlang to test the performance, which is 
> originally a benchmark for linux scheduler.
>      (Hackbench contains several groups; each groups contains 20 pairs 
> of senders and receivers; each sender needs to send some messages to 
> the 20 receivers in the same group. The performance is measured by the 
> time taken, less is better.)
>  
>      The tests are carried out on an Intel server with 2 quad-core 
> processors and 4G memory.
>      I am surprised with results I got:
>      (1) SMP enable +S 8
>      root@REDACTED:~/hackbench# \time ./run_one_erl.sh
>      Time is 62.260995
>      295.67user 110.62system 1:14.27elapsed 546%CPU (0avgtext+0avgdata 
> 0maxresident)k
>      11776inputs+8outputs (27major+90965minor)pagefaults 0swaps
>  
>       The performance is 62 sec and the oprofile shows 28% cpu time is 
> using in pthread_mutex_*.
>  
>       (2) SMP disable
>       root@REDACTED:~/hackbench <mailto:root@REDACTED:%7E/hackbench># \time 
> ./run_one_erl.sh "-smp disable"
>       Time is 54.14644
>       54.23user 0.33system 1:05.66elapsed 83%CPU (0avgtext+0avgdata 
> 0maxresident)k
>       3968inputs+8outputs (22major+36520minor)pagefaults 0swaps
>  
>       The performance is 54 sec and using only 83% cpu.
>  
>       So it seems the erlang has problems with using all the smp 
> resources for serious lock contention in smp scheduler. Am I right?
>       And because I am new to erlang, the hackbench.erl may be in bad 
> encoding, which will harm the performance. Can anyone help me review 
> my code?
>  
>       I attach both the original C version of hackbench and my erlang 
> version one.
>  
>       Thanks a lot!
>       (I am sorry If it is the wrong place to post this letter.)   
>
> -- 
> Best Regards,
> Jiang, Wei
> ------------------------------------------------------------------------
>
>
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