| Re: IDL calls C calls IDL? [message #62555 is a reply to message #62473] |
Mon, 15 September 2008 09:39  |
![Karl[1] is currently offline](theme/default/images/xoffline.png.pagespeed.ic.XRkd1fkXye.png "Karl[1] is currently offline")
Karl[1]
Messages: 79
Registered: October 2005
|
Member |
|
|
On Sep 12, 7:42 pm, "hotplainr...@gmail.com" <hotplainr...@gmail.com>
wrote:
> On Sep 11, 10:42 pm, Joost Aan de Brugh <joost...@gmail.com> wrote:
>
>
>
>> On Sep 11, 11:53 am, "hotplainr...@gmail.com" <hotplainr...@gmail.com>
>> wrote:
>
>>> Hey again,
>
>>> I've been thinking, I have code that does
>
>>> LINKIMAGE 'func' ,.....
>
>>> for t=0,tmax-1
>>> func(data)
>>> idl_function(data)
>>> endfor
>
>>> Is it possible to call idl_function from within C ?
>
>>> I want it to be like this
>
>>> In IDL:
>>> func(data)
>
>>> Then it passes onto C which does
>>> for (t=0; t<tmax;t++)
>>> {
>>> do whatever it does with data
>>> CALL IDL_FUNCTION(data)
>
>>> }
>
>>> This eliminates me calling func a few million times
>
>>> Can it be done?
>
>> Hello,
>
>> And in the above example, IDL takes the initiative, calls func (which
>> is, if I am right, a C function) and does its own IDL function. (IDL
>> calls C a million times).
>
>> Below, C takes the initiative, creates a forloop, and in each
>> iteration it does something with data and then has IDL do something
>> with data by calling IDL_FUNCTION. (C calls IDL a million times).
>
>> Which of them is less nasty is not easy to say. To figure out how to
>> call IDL from C is better known by C-people. So that could better be
>> asked in C-groups.
>
>> I do not know what your functions do with the data. But if the order
>> is not so important, you could try to do somthing like.
>
>> In C:
>> (t=0; t<tmax;t++)
>> {
>> C-code(data);
>
>> }
>
>> and in IDL:
>
>> Call_C_Code(data)
>
>> ; Now it's IDL time.
>> for t=0,tmax-1 do IDL_FUNCTION,data
>
>> But here, C does its whole task before IDL starts. This may be a
>> problem depending on the actions. It may be possible that C can
>> generate the actions that IDL can perform. For example:
>
>> In C:
>
>> (t=0; t<tmax;t++)
>> {
>> C-code(data,actions); // Actions is an output by C passed back to
>> IDL. Data is left unharmed.
>
>> }
>
>> in IDL:
>
>> Call_C_Code(data,actions)
>
>> ; Now it's IDL time.
>> for t=0,tmax-1 do begin
>> IDL_PERMORM_ACTION,actions,data
>> IDL_FUNCTION,data
>> End
>
>> Best regards,
>> Joost
>
> I should have phrased it in a better way.
>
> It is like this
>
> It all starts from within IDL
>
> So IDL does
>
> for t=0,tmax-1 do begin
> Part 1 of code written in IDL
> Part 2 of code written in IDL
> Part 3 of code written in IDL
> end
>
> Then I managed to convert part 1 and 3 into C and CUDA which is leaps
> ahead faster.
>
> So now it looks like this
> LINKIMAGE, 'Part1_C', 'file', 1, 'call_cuda'
> LINKIMAGE, 'Part3_C', 'file', 1, 'c_part3'
>
> for t=0,tmax-1 do begin
> Part 1 of code written in C that calls CUDA
> Part 2 of code written in IDL
> Part 3 of code written in C
> end
>
> Then I managed to combine the both Part 1 & 3
>
> LINKIMAGE, 'Part1+3_C', 'file', 1, 'call_cuda'
>
> for t=0,tmax-1 do begin
> Part (1+3) of code written in C & CUDA
> Part 2 of code written in IDL
> end
>
> Okay, so this is the nasty bit. Everytime I call Part(1+3), it calls
> the C function. There is no memory transfer because they share memory
> addresses, which is all great. However, that C function will allocate
> memory and transfer data to the graphics card because it is a normal
> CUDA procedure, allocate and transfer then execute computation kernel.
>
> The issue is it has to allocate and transfer data to the graphics
> card. It takes awhile especially when you have 434 MBs to send every
> iteration. That could easily be x4 = 1.5 Gigs of data to the GPU.
> Whats worse is that it sends the same data all the time.
>
> So imagine tmax=10^8, that is 10^8 * (the time to transfer to and
> back) = 10^8 * 0.01 = 10^6 seconds.
>
> My aim is for
>
> LINKIMAGE, 'fast_C', 'file', 1, 'call_cuda'
>
> Within IDL
>
> <some IDL commands>
> fast_C(..., ..., ...)
> <some IDL commands>
>
> Within the C code,
>
> Call_CUDA
> end of file
>
> Within CUDA code,
> Allocate memory and transfer data
>
> for (t=0; t<tmax;t++)
> {
> Part 1
> Part 3 // They don't necessarily have to be in order
> Transfer data from GPU to host
> CALL_IDL ( Part 2)
>
> }
>
> So I essentially have eliminated transfering to the GPU 10^8 times and
> thus a significant fraction of 10^6 seconds.
>
> Why don't I convert Part 2?
> I think its too hard for me to re-invent this wheel, its image writing
> code and some special code that is written by someone else
I think that there is a C function called IDL_Execute that you can
call from your C program that will let you run IDL statements.
See
http://idlastro.gsfc.nasa.gov/idl_html_help/Executing_IDL_St atements.html
or google for IDL_Execute.
Or read the IDL External Programming Guide
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
