-----Original Message----- From: Daniel Vetter daniel@ffwll.ch Sent: Tuesday, November 24, 2020 7:17 AM To: Jason Gunthorpe jgg@ziepe.ca Cc: Xiong, Jianxin jianxin.xiong@intel.com; Leon Romanovsky leon@kernel.org; linux-rdma@vger.kernel.org; dri- devel@lists.freedesktop.org; Doug Ledford dledford@redhat.com; Vetter, Daniel daniel.vetter@intel.com; Christian Koenig christian.koenig@amd.com Subject: Re: [PATCH rdma-core 3/5] pyverbs: Add dma-buf based MR support
On Mon, Nov 23, 2020 at 02:05:04PM -0400, Jason Gunthorpe wrote:
On Mon, Nov 23, 2020 at 09:53:02AM -0800, Jianxin Xiong wrote:
+cdef class DmaBuf:
- def __init__(self, size, unit=0):
"""Allocate DmaBuf object from a GPU device. This is done through theDRI device interface (/dev/dri/card*). Usually this+requires the
Please use /dev/dri/renderD* instead. That's the interface meant for unpriviledged rendering access. card* is the legacy interface with backwards compat galore, don't use.
Specifically if you do this on a gpu which also has display (maybe some testing on a local developer machine, no idea ...) then you mess with compositors and stuff.
Also wherever you copied this from, please also educate those teams that using /dev/dri/card* for rendering stuff is a Bad Idea (tm)
/dev/dri/renderD* is not always available (e.g. for many iGPUs) and doesn't support mode setting commands (including dumb_buf). The original intention here is to have something to support the new tests added, not for general compute.
effective user id being root or being a member of the 'video' group.:param size: The size (in number of bytes) of the buffer.:param unit: The unit number of the GPU to allocate the buffer from.:return: The newly created DmaBuf object on success."""self.dmabuf_mrs = weakref.WeakSet()self.dri_fd = open('/dev/dri/card'+str(unit), O_RDWR)args = bytearray(32)pack_into('=iiiiiiq', args, 0, 1, size, 8, 0, 0, 0, 0)ioctl(self.dri_fd, DRM_IOCTL_MODE_CREATE_DUMB, args)a, b, c, d, self.handle, e, self.size = unpack('=iiiiiiq',- args)
Yeah no, don't allocate render buffers with create_dumb. Every time this comes up I'm wondering whether we should just completely disable dma-buf operations on these. Dumb buffers are explicitly only for software rendering for display purposes when the gpu userspace stack isn't fully running yet, aka boot splash.
And yes I know there's endless amounts of abuse of that stuff floating around, especially on arm-soc/android systems.
One alternative is to use the GEM_CREATE method which can be done via the renderD* device, but the command is vendor specific, so the logic is a little bit more complex.
args = bytearray(12)pack_into('=iii', args, 0, self.handle, O_RDWR, 0)ioctl(self.dri_fd, DRM_IOCTL_PRIME_HANDLE_TO_FD, args)a, b, self.fd = unpack('=iii', args)args = bytearray(16)pack_into('=iiq', args, 0, self.handle, 0, 0)ioctl(self.dri_fd, DRM_IOCTL_MODE_MAP_DUMB, args);a, b, self.map_offset = unpack('=iiq', args);Wow, OK
Is it worth using ctypes here instead? Can you at least add a comment before each pack specifying the 'struct XXX' this is following?
Does this work with normal Intel GPUs, like in a Laptop? AMD too?
Christian, I would be very happy to hear from you that this entire work is good for AMD as well
I think the smallest generic interface for allocating gpu buffers which are more useful than the stuff you get from CREATE_DUMB is gbm. That's used by compositors to get bare metal opengl going on linux. Ofc Android has gralloc for the same purpose, and cros has minigbm (which isn't the same as gbm at all). So not so cool.
Again, would the "renderD* + GEM_CREATE" combination be an acceptable alternative? That would be much simpler than going with gbm and less dependency in setting up the testing evrionment.
The other generic option is using vulkan, which works directly on bare metal (without a compositor or anything running), and is cross vendor. So cool, except not used for compute, which is generally the thing you want if you have an rdma card.
Both gbm-egl/opengl and vulkan have extensions to hand you a dma-buf back, properly.
Compute is the worst, because opencl is widely considered a mistake (maybe opencl 3 is better, but nvidia is stuck on 1.2). The actually used stuff is cuda (nvidia-only), rocm (amd-only) and now with intel also playing we have xe (intel-only).
It's pretty glorious :-/
Also I think we discussed this already, but for actual p2p the intel patches aren't in upstream yet. We have some internally, but with very broken locking (in the process of getting fixed up, but it's taking time).
Cheers, Daniel
Edward should look through this, but I'm glad to see something like this
Thanks, Jason _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch