On Thu, 17 Aug 2023 at 12:13, Zeng, Oak <oak.zeng@xxxxxxxxx> wrote: > > > -----Original Message----- > > From: Dave Airlie <airlied@xxxxxxxxx> > > Sent: August 16, 2023 6:52 PM > > To: Felix Kuehling <felix.kuehling@xxxxxxx> > > Cc: Zeng, Oak <oak.zeng@xxxxxxxxx>; Christian König > > <christian.koenig@xxxxxxx>; Thomas Hellström > > <thomas.hellstrom@xxxxxxxxxxxxxxx>; Brost, Matthew > > <matthew.brost@xxxxxxxxx>; maarten.lankhorst@xxxxxxxxxxxxxxx; > > Vishwanathapura, Niranjana <niranjana.vishwanathapura@xxxxxxxxx>; Welty, > > Brian <brian.welty@xxxxxxxxx>; Philip Yang <Philip.Yang@xxxxxxx>; intel- > > xe@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx > > Subject: Re: Implement svm without BO concept in xe driver > > > > On Thu, 17 Aug 2023 at 08:15, Felix Kuehling <felix.kuehling@xxxxxxx> wrote: > > > > > > On 2023-08-16 13:30, Zeng, Oak wrote: > > > > I spoke with Thomas. We discussed two approaches: > > > > > > > > 1) make ttm_resource a central place for vram management functions such as > > eviction, cgroup memory accounting. Both the BO-based driver and BO-less SVM > > codes call into ttm_resource_alloc/free functions for vram allocation/free. > > > > *This way BO driver and SVM driver shares the eviction/cgroup logic, no > > need to reimplment LRU eviction list in SVM driver. Cgroup logic should be in > > ttm_resource layer. +Maarten. > > > > *ttm_resource is not a perfect match for SVM to allocate vram. It is still a > > big overhead. The *bo* member of ttm_resource is not needed for SVM - this > > might end up with invasive changes to ttm...need to look into more details > > > > > > Overhead is a problem. We'd want to be able to allocate, free and evict > > > memory at a similar granularity as our preferred migration and page > > > fault granularity, which defaults to 2MB in our SVM implementation. > > > > > > > > > > > > > > 2) svm code allocate memory directly from drm-buddy allocator, and expose > > memory eviction functions from both ttm and svm so they can evict memory > > from each other. For example, expose the ttm_mem_evict_first function from > > ttm side so hmm/svm code can call it; expose a similar function from svm side so > > ttm can evict hmm memory. > > > > > > I like this option. One thing that needs some thought with this is how > > > to get some semblance of fairness between the two types of clients. > > > Basically how to choose what to evict. And what share of the available > > > memory does each side get to use on average. E.g. an idle client may get > > > all its memory evicted while a busy client may get a bigger share of the > > > available memory. > > > > I'd also like to suggest we try to write any management/generic code > > in driver agnostic way as much as possible here. I don't really see > > much hw difference should be influencing it. > > > > I do worry about having effectively 2 LRUs here, you can't really have > > two "leasts". > > > > Like if we hit the shrinker paths who goes first? do we shrink one > > object from each side in turn? > > One way to solve this fairness problem is to create a driver agnostic drm_vram_mgr. Maintain a single LRU in drm_vram_mgr. Move the memory eviction/cgroups memory accounting logic from ttm_resource manager to drm_vram_mgr. Both BO-based driver and SVM driver calls to drm_vram_mgr to allocate/free memory. > > I am not sure whether this meets the 2M allocate/free/evict granularity requirement Felix mentioned above. SVM can allocate 2M size blocks. But BO driver should be able to allocate any arbitrary sized blocks - So the eviction is also arbitrary size. > > > > > Also will we have systems where we can expose system SVM but userspace > > may choose to not use the fine grained SVM and use one of the older > > modes, will that path get emulated on top of SVM or use the BO paths? > > > If by "older modes" you meant the gem_bo_create (such as xe_gem_create or amdgpu_gem_create), then today both amd and intel implement those interfaces using BO path. We don't have a plan to emulate that old mode on tope of SVM, afaict. I'm not sure how the older modes manifest in the kernel I assume as bo creates (but they may use userptr), SVM isn't a specific thing, it's a group of 3 things. coarse-grained SVM which I think is BO fine-grained SVM which is page level fine-grained system SVM which is HMM I suppose I'm asking about the previous versions and how they would operate in a system SVM capable system. Dave. > > Thanks, > Oak > > > > > Dave.
