From: "Zeng, Oak" <oak.zeng@intel.com>
To: "Christian König" <christian.koenig@amd.com>,
"Danilo Krummrich" <dakr@redhat.com>,
"Dave Airlie" <airlied@redhat.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Felix Kuehling" <felix.kuehling@amd.com>
Cc: "Brost, Matthew" <matthew.brost@intel.com>,
"Thomas.Hellstrom@linux.intel.com"
<Thomas.Hellstrom@linux.intel.com>,
"Welty, Brian" <brian.welty@intel.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"Ghimiray, Himal Prasad" <himal.prasad.ghimiray@intel.com>,
"Gupta, saurabhg" <saurabhg.gupta@intel.com>,
"Bommu, Krishnaiah" <krishnaiah.bommu@intel.com>,
"Vishwanathapura,
Niranjana" <niranjana.vishwanathapura@intel.com>,
"intel-xe@lists.freedesktop.org" <intel-xe@lists.freedesktop.org>
Subject: RE: Making drm_gpuvm work across gpu devices
Date: Tue, 23 Jan 2024 19:37:07 +0000 [thread overview]
Message-ID: <SA1PR11MB699192584C01A26C781E2F9992742@SA1PR11MB6991.namprd11.prod.outlook.com> (raw)
In-Reply-To: <2928ce36-06a6-4bee-b115-8dd61cc41dca@amd.com>
Thanks Christian. I have some comment inline below.
Danilo, can you also take a look and give your feedback? Thanks.
> -----Original Message-----
> From: Christian König <christian.koenig@amd.com>
> Sent: Tuesday, January 23, 2024 6:13 AM
> To: Zeng, Oak <oak.zeng@intel.com>; Danilo Krummrich <dakr@redhat.com>;
> Dave Airlie <airlied@redhat.com>; Daniel Vetter <daniel@ffwll.ch>
> Cc: Welty, Brian <brian.welty@intel.com>; dri-devel@lists.freedesktop.org; intel-
> xe@lists.freedesktop.org; Bommu, Krishnaiah <krishnaiah.bommu@intel.com>;
> Ghimiray, Himal Prasad <himal.prasad.ghimiray@intel.com>;
> Thomas.Hellstrom@linux.intel.com; Vishwanathapura, Niranjana
> <niranjana.vishwanathapura@intel.com>; Brost, Matthew
> <matthew.brost@intel.com>
> Subject: Re: Making drm_gpuvm work across gpu devices
>
> Hi Oak,
>
> Am 23.01.24 um 04:21 schrieb Zeng, Oak:
> > Hi Danilo and all,
> >
> > During the work of Intel's SVM code, we came up the idea of making
> drm_gpuvm to work across multiple gpu devices. See some discussion here:
> https://lore.kernel.org/dri-
> devel/PH7PR11MB70049E7E6A2F40BF6282ECC292742@PH7PR11MB7004.namprd
> 11.prod.outlook.com/
> >
> > The reason we try to do this is, for a SVM (shared virtual memory across cpu
> program and all gpu program on all gpu devices) process, the address space has
> to be across all gpu devices. So if we make drm_gpuvm to work across devices,
> then our SVM code can leverage drm_gpuvm as well.
> >
> > At a first look, it seems feasible because drm_gpuvm doesn't really use the
> drm_device *drm pointer a lot. This param is used only for printing/warning. So I
> think maybe we can delete this drm field from drm_gpuvm.
> >
> > This way, on a multiple gpu device system, for one process, we can have only
> one drm_gpuvm instance, instead of multiple drm_gpuvm instances (one for
> each gpu device).
> >
> > What do you think?
>
> Well from the GPUVM side I don't think it would make much difference if
> we have the drm device or not.
>
> But the experience we had with the KFD I think I should mention that we
> should absolutely *not* deal with multiple devices at the same time in
> the UAPI or VM objects inside the driver.
>
> The background is that all the APIs inside the Linux kernel are build
> around the idea that they work with only one device at a time. This
> accounts for both low level APIs like the DMA API as well as pretty high
> level things like for example file system address space etc...
Yes most API are per device based.
One exception I know is actually the kfd SVM API. If you look at the svm_ioctl function, it is per-process based. Each kfd_process represent a process across N gpu devices. Cc Felix.
Need to say, kfd SVM represent a shared virtual address space across CPU and all GPU devices on the system. This is by the definition of SVM (shared virtual memory). This is very different from our legacy gpu *device* driver which works for only one device (i.e., if you want one device to access another device's memory, you will have to use dma-buf export/import etc).
We have the same design requirement of SVM. For anyone who want to implement the SVM concept, this is a hard requirement. Since now drm has the drm_gpuvm concept which strictly speaking is designed for one device, I want to see whether we can extend drm_gpuvm to make it work for both single device (as used in xe) and multipe devices (will be used in the SVM code). That is why I brought up this topic.
>
> So when you have multiple GPUs you either have an inseparable cluster of
> them which case you would also only have one drm_device. Or you have
> separated drm_device which also results in separate drm render nodes and
> separate virtual address spaces and also eventually separate IOMMU
> domains which gives you separate dma_addresses for the same page and so
> separate GPUVM page tables....
I am thinking we can still make each device has its separate drm_device/render node/iommu domains/gpu page table. Just as what we have today. I am not plan to change this picture.
But the virtual address space will support two modes of operation:
1. one drm_gpuvm per device. This is when svm is not in the picture
2. all devices in the process share one single drm_gpuvm, when svm is in the picture. In xe driver design, we have to support a mixture use of legacy mode (such as gem_create and vm_bind) and svm (such as malloc'ed memory for gpu submission). So whenever SVM is in the picture, we want one single process address space across all devices. Drm_gpuvm doesn't need to be aware of those two operation modes. It is driver's responsibility to use different mode.
For example, in mode #1, a driver's vm structure (such as xe_vm) can inherit from drm_gpuvm. In mode #2, a driver's svm structure (xe_svm in this series: https://lore.kernel.org/dri-devel/20240117221223.18540-1-oak.zeng@intel.com/) can inherit from drm_gpuvm while each xe_vm (still a per-device based struct) will just have a pointer to the drm_gpuvm structure. This way when svm is in play, we build a 1 process:1 mm_struct:1 xe_svm:N xe_vm correlations which means shared address space across gpu devices.
This requires some changes of drm_gpuvm design:
1. The drm_device *drm pointer, in mode #2 operation, this can be NULL, means this drm_gpuvm is not for specific gpu device
2. The common dma_resv object: drm_gem_object *r_obj. *Does one dma_resv object allocated/initialized for one device work for all devices*? From first look, dma_resv is just some CPU structure maintaining dma-fences. So I guess it should work for all devices? I definitely need you to comment.
>
> It's up to you how to implement it, but I think it's pretty clear that
> you need separate drm_gpuvm objects to manage those.
As explained above, I am thinking of one drm_gpuvm object across all devices when SVM is in the picture...
>
> That you map the same thing in all those virtual address spaces at the
> same address is a completely different optimization problem I think.
Not sure I follow here... the requirement from SVM is, one virtual address points to same physical backing store. For example, whenever CPU or any GPU device access this virtual address, it refers to the same physical content. Of course the physical backing store can be migrated b/t host memory and any of the GPU's device memory, but the content should be consistent.
So we are mapping same physical content to the same virtual address in either cpu page table or any gpu device's page table...
> What we could certainly do is to optimize hmm_range_fault by making
> hmm_range a reference counted object and using it for multiple devices
> at the same time if those devices request the same range of an mm_struct.
>
Not very follow. If you are trying to resolve a multiple devices concurrent access problem, I think we should serialize concurrent device fault to one address range. The reason is, during device fault handling, we might migrate the backing store so hmm_range->hmm_pfns[] might have changed after one device access it.
> I think if you start using the same drm_gpuvm for multiple devices you
> will sooner or later start to run into the same mess we have seen with
> KFD, where we moved more and more functionality from the KFD to the DRM
> render node because we found that a lot of the stuff simply doesn't work
> correctly with a single object to maintain the state.
As I understand it, KFD is designed to work across devices. A single pseudo /dev/kfd device represent all hardware gpu devices. That is why during kfd open, many pdd (process device data) is created, each for one hardware device for this process. Yes the codes are a little complicated.
Kfd manages the shared virtual address space in the kfd driver codes, like the split, merging etc. Here I am looking whether we can leverage the drm_gpuvm code for those functions.
As of the shared virtual address space across gpu devices, it is a hard requirement for svm/system allocator (aka malloc for gpu program). We need to make it work either at driver level or drm_gpuvm level. Drm_gpuvm is better because the work can be shared b/t drivers.
Thanks a lot,
Oak
>
> Just one more point to your original discussion on the xe list: I think
> it's perfectly valid for an application to map something at the same
> address you already have something else.
>
> Cheers,
> Christian.
>
> >
> > Thanks,
> > Oak
next prev parent reply other threads:[~2024-01-23 19:37 UTC|newest]
Thread overview: 123+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-17 22:12 [PATCH 00/23] XeKmd basic SVM support Oak Zeng
2024-01-17 22:12 ` [PATCH 01/23] drm/xe/svm: Add SVM document Oak Zeng
2024-01-17 22:12 ` [PATCH 02/23] drm/xe/svm: Add svm key data structures Oak Zeng
2024-01-17 22:12 ` [PATCH 03/23] drm/xe/svm: create xe svm during vm creation Oak Zeng
2024-01-17 22:12 ` [PATCH 04/23] drm/xe/svm: Trace svm creation Oak Zeng
2024-01-17 22:12 ` [PATCH 05/23] drm/xe/svm: add helper to retrieve svm range from address Oak Zeng
2024-01-17 22:12 ` [PATCH 06/23] drm/xe/svm: Introduce a helper to build sg table from hmm range Oak Zeng
2024-04-05 0:39 ` Jason Gunthorpe
2024-04-05 3:33 ` Zeng, Oak
2024-04-05 12:37 ` Jason Gunthorpe
2024-04-05 16:42 ` Zeng, Oak
2024-04-05 18:02 ` Jason Gunthorpe
2024-04-09 16:45 ` Zeng, Oak
2024-04-09 17:24 ` Jason Gunthorpe
2024-04-23 21:17 ` Zeng, Oak
2024-04-24 2:31 ` Matthew Brost
2024-04-24 13:57 ` Jason Gunthorpe
2024-04-24 16:35 ` Matthew Brost
2024-04-24 16:44 ` Jason Gunthorpe
2024-04-24 16:56 ` Matthew Brost
2024-04-24 17:48 ` Jason Gunthorpe
2024-04-24 13:48 ` Jason Gunthorpe
2024-04-24 23:59 ` Zeng, Oak
2024-04-25 1:05 ` Jason Gunthorpe
2024-04-26 9:55 ` Thomas Hellström
2024-04-26 12:00 ` Jason Gunthorpe
2024-04-26 14:49 ` Thomas Hellström
2024-04-26 16:35 ` Jason Gunthorpe
2024-04-29 8:25 ` Thomas Hellström
2024-04-30 17:30 ` Jason Gunthorpe
2024-04-30 18:57 ` Daniel Vetter
2024-05-01 0:09 ` Jason Gunthorpe
2024-05-02 8:04 ` Daniel Vetter
2024-05-02 9:11 ` Thomas Hellström
2024-05-02 12:46 ` Jason Gunthorpe
2024-05-02 15:01 ` Thomas Hellström
2024-05-02 19:25 ` Zeng, Oak
2024-05-03 13:37 ` Jason Gunthorpe
2024-05-03 14:43 ` Zeng, Oak
2024-05-03 16:28 ` Jason Gunthorpe
2024-05-03 20:29 ` Zeng, Oak
2024-05-04 1:03 ` Dave Airlie
2024-05-06 13:04 ` Daniel Vetter
2024-05-06 23:50 ` Matthew Brost
2024-05-07 11:56 ` Jason Gunthorpe
2024-05-06 13:33 ` Jason Gunthorpe
2024-04-09 17:33 ` Matthew Brost
2024-01-17 22:12 ` [PATCH 07/23] drm/xe/svm: Add helper for binding hmm range to gpu Oak Zeng
2024-01-17 22:12 ` [PATCH 08/23] drm/xe/svm: Add helper to invalidate svm range from GPU Oak Zeng
2024-01-17 22:12 ` [PATCH 09/23] drm/xe/svm: Remap and provide memmap backing for GPU vram Oak Zeng
2024-01-17 22:12 ` [PATCH 10/23] drm/xe/svm: Introduce svm migration function Oak Zeng
2024-01-17 22:12 ` [PATCH 11/23] drm/xe/svm: implement functions to allocate and free device memory Oak Zeng
2024-01-17 22:12 ` [PATCH 12/23] drm/xe/svm: Trace buddy block allocation and free Oak Zeng
2024-01-17 22:12 ` [PATCH 13/23] drm/xe/svm: Handle CPU page fault Oak Zeng
2024-01-17 22:12 ` [PATCH 14/23] drm/xe/svm: trace svm range migration Oak Zeng
2024-01-17 22:12 ` [PATCH 15/23] drm/xe/svm: Implement functions to register and unregister mmu notifier Oak Zeng
2024-01-17 22:12 ` [PATCH 16/23] drm/xe/svm: Implement the mmu notifier range invalidate callback Oak Zeng
2024-01-17 22:12 ` [PATCH 17/23] drm/xe/svm: clean up svm range during process exit Oak Zeng
2024-01-17 22:12 ` [PATCH 18/23] drm/xe/svm: Move a few structures to xe_gt.h Oak Zeng
2024-01-17 22:12 ` [PATCH 19/23] drm/xe/svm: migrate svm range to vram Oak Zeng
2024-01-17 22:12 ` [PATCH 20/23] drm/xe/svm: Populate svm range Oak Zeng
2024-01-17 22:12 ` [PATCH 21/23] drm/xe/svm: GPU page fault support Oak Zeng
2024-01-23 2:06 ` Welty, Brian
2024-01-23 3:09 ` Zeng, Oak
2024-01-23 3:21 ` Making drm_gpuvm work across gpu devices Zeng, Oak
2024-01-23 11:13 ` Christian König
2024-01-23 19:37 ` Zeng, Oak [this message]
2024-01-23 20:17 ` Felix Kuehling
2024-01-25 1:39 ` Zeng, Oak
2024-01-23 23:56 ` Danilo Krummrich
2024-01-24 3:57 ` Zeng, Oak
2024-01-24 4:14 ` Zeng, Oak
2024-01-24 6:48 ` Christian König
2024-01-25 22:13 ` Danilo Krummrich
2024-01-24 8:33 ` Christian König
2024-01-25 1:17 ` Zeng, Oak
2024-01-25 1:25 ` David Airlie
2024-01-25 5:25 ` Zeng, Oak
2024-01-26 10:09 ` Christian König
2024-01-26 20:13 ` Zeng, Oak
2024-01-29 10:10 ` Christian König
2024-01-29 20:09 ` Zeng, Oak
2024-01-25 11:00 ` 回复：Making " 周春明(日月)
2024-01-25 17:00 ` Zeng, Oak
2024-01-25 17:15 ` Making " Felix Kuehling
2024-01-25 18:37 ` Zeng, Oak
2024-01-26 13:23 ` Christian König
2024-01-25 16:42 ` Zeng, Oak
2024-01-25 18:32 ` Daniel Vetter
2024-01-25 21:02 ` Zeng, Oak
2024-01-26 8:21 ` Thomas Hellström
2024-01-26 12:52 ` Christian König
2024-01-27 2:21 ` Zeng, Oak
2024-01-29 10:19 ` Christian König
2024-01-30 0:21 ` Zeng, Oak
2024-01-30 8:39 ` Christian König
2024-01-30 22:29 ` Zeng, Oak
2024-01-30 23:12 ` David Airlie
2024-01-31 9:15 ` Daniel Vetter
2024-01-31 20:17 ` Zeng, Oak
2024-01-31 20:59 ` Zeng, Oak
2024-02-01 8:52 ` Christian König
2024-02-29 18:22 ` Zeng, Oak
2024-03-08 4:43 ` Zeng, Oak
2024-03-08 10:07 ` Christian König
2024-01-30 8:43 ` Thomas Hellström
2024-01-29 15:03 ` Felix Kuehling
2024-01-29 15:33 ` Christian König
2024-01-29 16:24 ` Felix Kuehling
2024-01-29 16:28 ` Christian König
2024-01-29 17:52 ` Felix Kuehling
2024-01-29 19:03 ` Christian König
2024-01-29 20:24 ` Felix Kuehling
2024-02-23 20:12 ` Zeng, Oak
2024-02-27 6:54 ` Christian König
2024-02-27 15:58 ` Zeng, Oak
2024-02-28 19:51 ` Zeng, Oak
2024-02-29 9:41 ` Christian König
2024-02-29 16:05 ` Zeng, Oak
2024-02-29 17:12 ` Thomas Hellström
2024-03-01 7:01 ` Christian König
2024-01-17 22:12 ` [PATCH 22/23] drm/xe/svm: Add DRM_XE_SVM kernel config entry Oak Zeng
2024-01-17 22:12 ` [PATCH 23/23] drm/xe/svm: Add svm memory hints interface Oak Zeng
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