Re: [ViennaCL-devel] Implementation of multi_inner_prod

[Philippe T. <phi...@gm...>]

Ok, thanks!
This sounds reasonable indeed.

Philippe


2014-06-26 23:51 GMT+02:00 Karl Rupp <ru...@iu...>:

> Hi,
>
> the cases 5, 6, and 7 are handled by running a kernel for four vectors,
> then subtract '4' and run a dedicated kernel on the remaining 1, 2, or 3
> vectors. This could also be handled by a generated kernel, yes, but I
> haven't implemented this for two reasons:
>  1. less kernels to compile
>  2. less implementation effort
>
> One single kernel is not possible for arbitrary values of vectors. Eight
> vectors turned out to be a reasonable upper bound because the overhead is
> less than 12.5% over the ideal case already, but at the same time the
> kernel still works for older GPUs with limited amounts of shared memory.
>
> Best regards,
> Karli
>
>
>
> On 06/26/2014 11:09 PM, Philippe Tillet wrote:
>
>> I'll add something. I assume that multiple kernels are launched thanks
>> to current_index. Wouldn't it be better to launch one single kernel ? I
>> think that a lot of users would prefer to have better performance for
>> perhaps a slightly longer JIT overhead (since we'll provide a caching
>> mechanism).
>>
>> Philippe
>>
>>
>> 2014-06-26 23:07 GMT+02:00 Philippe Tillet <phi...@gm...
>> <mailto:phi...@gm...>>:
>>
>>
>>     Hello!
>>
>>     I note this in the implementation of multi_inner_prod:
>>
>>                switch (vec_tuple.const_size() - current_index)
>>                {
>>                  case 7:
>>                  case 6:
>>                  case 5:
>>                  case 4:
>>                    //do stuff
>>
>>     However, there is a test for 5,6,7 so I assume that these have to be
>>     implemented somehow. Could I have more details on why there is no
>>     specific kernel for these three cases?
>>
>>     NB : This is the very last thing that has to be done before I can
>>     push the new device-specific OpenCL backend. All the tests pass
>>     except multi_inner_prod for tuple_size >= 5. :)
>>
>>     Philippe
>>
>>
>>
>>
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>