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Date: Sun, 13 Jan 2013 12:23:39 -0200
From: Claudio André <>
Subject: Re: Changes to common-opencl.c

Em 12-01-2013 23:48, Lukas Odzioba escreveu:
> In my opinion we should have some kind of "framework" that can handle 
> multigpu support itself. Some time ago I tried to move function 
> finding "best" GWS/LWS to common-opencl but it didn't ended well and 
> now we still have bad situation where almost each format have a lot of 
> copy pasted code for doing that. When it comes to multigpu there will 
> be more copy pasting and this is not a good thing. Ideally we should 
> be able to run code with different in speed gpus and have almost no 
> speed regression (I mean that sum of speeds from testing gpus 
> separately should be equal multigpu mode). This is not easy at all 
> especially in one thread, but less problematic than the same thing in 
> cuda. Maybe it will require some changes in fmt_ interface, or could 
> be done by some "task manager" working inside crypt() function to 
> divide data and gather results from gpus. 

I agree, but I need to have a good undestanding about what is really 
necessary to suggest / change. Now, only Sayantan produced muti-gpu 
code. So, I intend to create the possibility and latter create something 
multi-gpu in order to see what is possible/necessary.

My fellings is that without core modifications we will have some speed 
regression (as you said in [1]). Better than nothing but not perfect.

For now, I'm only handling better a multi-gpu environment. Using only 
one thread, the format creator still has to figure out which LWS/GWS 
pick in order to result in [1]. Maybe using Sayantan work and your idea 
in opencl_find_best_workgroup() is enought. Now, I have no idea if it is 

[1] - "have almost no speed regression ('you' mean that sum of speeds 
from testing gpus separately should be equal multigpu mode)"

>> Problems:
>> - hot-plug is not going to be handled. Well, it is not handled now too.
> What do you mean by hotplug? Adding gpus while john is runnig?



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