Re: multithreading

Hi John,


 From the distance, your situation looks very much as if one thread were 
doing all the work and the others are either dead or doing nothing 
useful. You have definitely thought of that, starting up "htop" or "Task 
Manager" to check whether all the CPU cores are busy all the time as 
planned?


Let me mention that the debugger performs a bunch of other operations at 
each step (including resuming and stopping all the threads), thus, it 
can easily disturb your experiment in finding out where the time goes.


If I were you, I would measure where the CPU is spending his time, 
something along the following lines is sufficient for a start:

const FXTime start_ns = FXDate::universalDate().getTime();

... some code

const FXTime end_ns = FXDate::universalDate().getTime();

const double time_seconds = 1e-9 * (end_ns - start_ns);


In a multithreaded code one might be interested in:
a) recording the start and stop times of each thread.
b) having a separate log file for each thread - this helps to see 
whether the threads are performing similarly.



best regards,

Andrei

Am 20.11.2022 um 20:57 schrieb John Selverian:
>
> It takes a very short time to fill the FXArray, pass the data and 
> start the threads. When I step through the code with the debugger 
> these steps combined take about 2 second per thread.
>
> I guess I’ll stick with 1 thread.
>
> *From:* JVZ <[email protected]>
> *Sent:* Sunday, November 20, 2022 2:07 PM
> *To:* [email protected]; Enno Rehling 
> <[email protected]>
> *Subject:* Re: [Foxgui-users] multithreading
>
>
> ...amdahls law. Indeed. There is always a lot of serial stuff in any code.
> Whats worse is that the serial part has its 'working set' mostly 
> cache-resident.
>
> Farming a chunk of work out to other threads first has to make up for 
> the transfer of cached data to the other threads. This needs to happen 
> before the other threads start to actually help, rather than impair, 
> performance.
>
> Again the longer the cpujob is the less this transient behaviour hurts.
>
> Its why i would suggest vectorization first. It almost always helps..
>
>
>
>
> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>
>
>
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