I am converting a Carbon app to Cocoa (where I'm a newbie). The Carbon app was multithreaded and heavily dependent on cblas and clapack. It worked well and was fully twice as fast with 2 CPUs as with 1. However, the code was becoming increasingly obsolete.
I now have a Cocoa [ObjectiveC++] version, also multithreaded, targeting Leopard and with Garbage Collection required (Xcode 3.1.3). In place of BLAS and LAPACK, I am now using the public-domain Eigen library, sacrificing some speed for readability. My (very embarrassing) problem is that this Cocoa app is monotonically *slower* with increasing number of CPUs. I have tried 1, 2 and 4 CPUs, creating k NSOperations for k CPUs and adding them to an NSOperationQueue. Obviously, the question is where to look for the cause. My experience with Instruments is quite limited. Also, in this app, each NSOperation is identical, processing 1/k of the input data with identical functions (hence, identical function names). FWIW, my old Carbon app is 18x faster than my fastest Cocoa version (28 sec vs. 9 min), partly due to Eigen, of course. With Instruments, some of the results I see are 1) With 1 CPU (NSOperation not used), I get 50% of CPU-time devoted to auto_collection_thread which I presume means Garbage Collection. Is this normal? It seems excessive. 2) With 2 CPUs, I get 26% of CPU-time for auto_collection_thread and another 26% for mach_msg_trap --> CFRunLoopSpecific (apparently back to Carbon again). 3) The compute-intensive function that was explicitly multithreaded takes 3.4% of the time with 1 CPU and 1.7% with 2 CPUs, bearing in mind that the latter runtime is about 25% longer overall. 4) Even though Instruments (Sampler, CPU Monitor, Cocoa Events) is using "separate by thread", it does not show separate threads for my k NSOperations; it still collects function names together so I cannot tell one NSOperation from another. Can anyone suggest what I should try next? I was really hoping that multithreading would speed things up (as it did in my Carbon version). Thanks for any tips. -- Mike McLaughlin _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
