Le 23/08/2012 13:10, Andreas Kloeckner a écrit :
Vincent Danjean <vdanjean.ml(a)free.fr> writes:
>> I think this is a design flaws in the specs.
>> An ICD Loader has no information at all (unless we decide to hardcode
>> some of them) about the supported OpenCL functions by the loaded ICD.
The ICD loader *could* call the implementation's platform version
GetInfo, though, and route the CreateImage calls accordingly?
But if that's not accepted practice among ICD loaders, it's not useful,
as PyOpenCL has to work against all of them.
Is any of you on the CL committee and able to let them know that they
screwed up? If not, I can reach see if I can reach someone...
We are not in the CL committee at all. Brice was working with OpenCL
and decided to write a free OCL ICD loader when he see that none was
existing and that a few reverse engineering would allow him to write one.
He put me in the loop as I'm more experimented with software packaging.
>> An ICD Loader merely get a address of of array of function
>> even does not know the size of the array it gets. This means, there is
>> no reliable way to know if the address we got for a 1.2 function is
>> garbage (belong the end of the table of an 1.1 implementation) or
>> Looking at version advertised by the ICD implementation is not a
>> solution: Intel implementation advertises 1.1 but implement (part of)
That seems perfectly within-spec. I.e. "call the 1.2 bits at your own
risk". I don't see the ICD loader under any obligation to make it
possible to call the 1.2 bits if the ICD advertises 1.1.
This means that our ICD loader will not be useful (and used) when
vendors get place in the function pointer structure before these
extensions are normalized into a future OpenCL spec.
Looking at what happens into the structure (places not used anymore
between official OpenCL function 1.0 and 1.1, similar between OpenCL
1.1 and OpenCL 1.2), this is not theoretical at all.
>> I'm willing to add/patch anything required in ocl-icd. We
can add some
>> more functions to the interface (it means that a program using these
>> functions will not work with other OpenCL ICD loader) or provides
>> them in an additional library (so that it works with any ICD Loader
>> But, for now, I see no other way than using hardcoded information.
>> If we go this path, we should think about which information we want
>> exactly and how we want them to be presented (ie API/ABI)
>> What I can propose is that, for any public symbol, we try to look
>> if the corresponding function exists in the targeted ICD. Some
>> sanity checks can be done automatically (non-null pointer, ...)
>> but some hard-coded information will be required.
>> I also ask me how/if we can divert the internal function pointer
>> structure provided by the implementation in order to fully fill
>> a whole structure (with error functions for the missing ones).
>> I think that is is feasible. But that it would be possible for
>> a strange ICD implementation to respect the standard and break
>> with what I imagine (ie my implementation would be border-line
>> with respect to the ABI specifications)
>> About the specific problem of clCreateImage, I tried to look at
>> it. If I understand correctly,
>> OpenCL 1.1 defines clCreateImage2D and clCreateImage3D
>> OpenCL 1.2 defines clCreateImage and deprecates clCreateImage2D
>> and clCreateImage3D
>> I.e, contrary to the initial message, I do not think that a
>> prototype changes (this would be a severe bug with respect to
>> ICD Loader specifications). But we have 2/3 functions with
>> similar prototypes, some provided by some implementations,
>> other provided by other implementations.
What a nightmare.
>> But, for now, I do not think there is any way an implementation
>> can currently reliably detect at run-time if an specific plate-form
>> implement or not theses functions.
(Not sure I agree here--see first comment.)
In any case, the design of ICD is done so that different versions of
OpenCL ICD can be loaded by the same loader. It means that the
OpenCL version cannot be chosen/checked at compile-time but only at
Supported OpenCL version can be, more or less, obtained by requesting
the plate-form version, we must got "OpenCL 1.X ..."
Using this, OpenCL software can decide to :
- ask for another plate-form (if available)
- adapt its code to the advertized OpenCL version
this can perhaps be done in a mid-layer that will be reusable
- crash/emit an error message
One must take care that some implementation does not implement deprecated
functions. For example, Intel OpenCL 1.1 implementation does not provide
any function for the deprecated clSetCommandQueueProperty...
In my opinion, what is missing in the current spec are (at least):
- a way to know the size of the structure we got from the ICD
An easy way to do so can be to give this size (in bytes or in entries)
as a long stored just before the current structure *and* advertize this
by declaring an extension in the ICD.
- a way for a program to know if a plate-form implements or not any
function. The clGetExtensionFunctionAddressForPlatform might be the
solution (but the previous information is required)
=> I will try to do it correctly for the next ocl-icd release
adding some hardcoded information if needed.
- a way for a program to require a specific (minimum/exact/maximum)
OpenCL version. In fact, this can be done by iterating over the
Vincent Danjean Adresse: Laboratoire d'Informatique de Grenoble
Téléphone: +33 4 76 61 20 11 ENSIMAG - antenne de Montbonnot
Fax: +33 4 76 61 20 99 ZIRST 51, avenue Jean Kuntzmann
Email: Vincent.Danjean(a)imag.fr 38330 Montbonnot Saint Martin