Re: Interacting with coherent memory on external devices

[Rik van Riel <riel@redhat.com>]

On 04/21/2015 08:50 PM, Christoph Lameter wrote:
> On Tue, 21 Apr 2015, Jerome Glisse wrote:

>> So big use case here, let say you have an application that rely on a
>> scientific library that do matrix computation. Your application simply
>> use malloc and give pointer to this scientific library. Now let say
>> the good folks working on this scientific library wants to leverage
>> the GPU, they could do it by allocating GPU memory through GPU specific
>> API and copy data in and out. For matrix that can be easy enough, but
>> still inefficient. What you really want is the GPU directly accessing
>> this malloced chunk of memory, eventualy migrating it to device memory
>> while performing the computation and migrating it back to system memory
>> once done. Which means that you do not want some kind of filesystem or
>> anything like that.
> 
> With a filesystem the migration can be controlled by the application.

Which is absolutely the wrong thing to do when using the "GPU"
(or whatever co-processor it is) transparently from libraries,
without the applications having to know about it.

Your use case is legitimate, but so is this other case.

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