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Date: Thu, 20 Dec 2012 21:28:18 +0100
From: magnum <>
Subject: Re: Opencl build from binary

On 20 Dec, 2012, at 20:51 , Claudio André <> wrote:
> Em 19-12-2012 17:28, magnum escreveu:
>> I have committed this. I think we should take this opportunity to think about another thing now that we hack around in there anyway: How can we support using multiple devices? Sayantan's mscash2 supports multiple devices already, but only by hacking the format source. We should add proper support using --platform and --device.
>> Maybe we should drop the --platform notation though? On Bull (where nvidia is device #0), that would mean the Tahiti would become device #1 instead of "platform 1, device 0" and the CPUs would become device #2.
>> And maybe we should start from 1 instead - I think Hashcat would list them as device 1 and 2 with no platform notation.
>> Having done that, the syntax for multiple devices becomes much easier. You could say --device=1 or --device=1,2 and perhaps even ranges like --device=1-8 for vcl use. If we wanted to we could also support types, so --device=gpus would mean "use all available GPU devices".
>> That's for the options syntax. Now, how would a format use this, or know about this? Should we support using a group of heterogenous devices? What would a well thought out interface to common-opencl.c look like?
> Very nice resource to have. I volunteer to help.
> - What kind of problems Sayantan faced?

His format seem to work fine, except it doesn't have support from common-opencl.c so you need to edit it and un-comment some lines in init() to make it use more than one device. The mscash2-opencl format does 103003 c/s on 7970 or 31679 c/s on the 570. If you just do this...

diff --git a/src/opencl_mscash2_fmt.c b/src/opencl_mscash2_fmt.c
index 04cb249..d62d50a 100644
--- a/src/opencl_mscash2_fmt.c
+++ b/src/opencl_mscash2_fmt.c
@@ -205,10 +205,10 @@ static void init(struct fmt_main *self)
-       select_device(platform_id,ocl_gpu_id);
+       //select_device(platform_id,ocl_gpu_id);
        ///Select devices select_device(int platform_no, int device_no). You may select multiple devices for faster cracking spped. Please See common_opencl_pbkdf2.h
-       //select_device(1,0);
-       //select_device(0,0);
+       select_device(1,0);
+       select_device(0,0);
        ///select default platform=0 and default device=0
        //select_default_device(); will use both, and do 127563 c/s, which is 95% of the single-figures added together. I bet it's better if you use two or more devices of the same model.

I think common-opencl.c is half-heartedly prepared to handle several devices - for instance, device[] and queue[] and such things are arrays already. But someone need to digest it and add the missing pieces (and modify some of the existing).

> Are we going to create more threads to control (each) device crypt_all?

Maybe later, I'm not sure. But it's not really needed for slow formats like this. You can either just enqueue jobs for several devices in one go, or juggle them.


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