Hi Harshad,
On Mon 20 Jan 2014 10:10:26 AM MST, Harshad Sahasrabudhe wrote:
Hi Dominic,
We use external libraries such as MAGMA and cuSPARSE. It looks like
they use the runtime API as you mentioned above. At the moment,
conflict is between the two instances of PETSc that we run (one each
for real and complex). We are planning to write some code in CUDA and
will use the driver API if need be.
Karl seems to know how to resolve the conflict between the two instances
of PETSc. I'm not sure how exactly he is going to resolve this issue but
apparently he thinks it's rather easy to do.
Does moving to the driver API look like something that can be included
in PETSc 3.5?
I doubt it given the challenge of dealing with third party libraries via
the driver API. Quite possible somebody with a better understanding of
the PETSc roadmap has a more informed opinion.
Cheers,
Dominic
Harshad
On Mon, Jan 20, 2014 at 11:27 AM, Dominic Meiser <[email protected]
<mailto:[email protected]>> wrote:
Hi Jed, Harshad,
A different solution to the problem of PETSc and a user code
stepping on each other's feet with cudaSetDevice might be to use
the CUDA driver API for device selection rather than the runtime
API. If we were to explicitly manage a PETSc CUDA context using
the driver API we can control what devices are being used without
interfering with the mechanisms used by other parts of a client
code for CUDA device selection (e.g. cudaSetDevice). PETSc's
device management would be completely decoupled from the rest of
an application.
Of course this approach can be combined with lazy initialization
as proposed by Karl. Whenever the first device function is called
we create the PETSc CUDA context. The advantages of lazy
initialization mentioned by Karl and Jed ensue (e.g. ability to
run on machines without GPUs provided one is not using GPU
functionality).
Another advantage of a solution using the driver API is that
device and context management would be very similar between CUDA
and OpenCL backends.
I realize that this proposal might be impractical as a near term
solution since it involves a pretty major refactor of the CUDA
context infrastructure. Furthermore, as far as I can tell, third
party libraries that we rely on (e.g. cusp and cusparse) assume
the runtime api. Perhaps these difficulties can be overcome?
A possible near term solution would be to turn this around and to
have applications with advanced device selection requirements use
the driver API. Harshad, I'm not familiar with your code but would
it be possible for you to use the driver API on your end to avoid
conflicts with cudaSetDevice calls inside PETSc?
Cheers,
Dominic
On 01/14/2014 09:27 AM, Harshad Sahasrabudhe wrote:
Hi Jed,
Sometime back we talked about an interface which could handle
other libraries calling cudaSetDevice simultaneously with
PETSc. For example, in our case 2 different instances of PETSc
calling cudaSetDevice.
>Sure, but how will we actually share the device between
libraries? What
>if the other library was not PETSc, but something else, and
they also
>called cudaSetDevice, but with a different default mapping
strategy?
>We need an interface that handles this case.
Do we already have any solution for this? If not, can we start
looking at this case?
Thanks,
Harshad
--
Dominic Meiser
Tech-X Corporation
5621 Arapahoe Avenue
Boulder, CO 80303
USA
Telephone: 303-996-2036
Fax: 303-448-7756
www.txcorp.com <http://www.txcorp.com>
--
Dominic Meiser
Tech-X Corporation
5621 Arapahoe Avenue
Boulder, CO 80303
USA
Telephone: 303-996-2036
Fax: 303-448-7756
www.txcorp.com
