On Fri, Dec 20, 2019 at 01:45:33PM +0000, Jason Gunthorpe wrote:
On Wed, Dec 18, 2019 at 02:41:47PM -0800, Niranjana Vishwanathapura wrote:> > +static u32 i915_svm_build_sg(struct i915_address_space *vm, > > + struct hmm_range *range, > > + struct sg_table *st) > > +{ > > + struct scatterlist *sg; > > + u32 sg_page_sizes = 0; > > + u64 i, npages; > > + > > + sg = NULL; > > + st->nents = 0; > > + npages = (range->end - range->start) / PAGE_SIZE; > > + > > + /* > > + * No need to dma map the host pages and later unmap it, as > > + * GPU is not allowed to access it with SVM. > > + * XXX: Need to dma map host pages for integrated graphics while > > + * extending SVM support there. > > + */ > > + for (i = 0; i < npages; i++) { > > + u64 addr = range->pfns[i] & ~((1UL << range->pfn_shift) - 1); > > + > > + if (sg && (addr == (sg_dma_address(sg) + sg->length))) { > > + sg->length += PAGE_SIZE; > > + sg_dma_len(sg) += PAGE_SIZE; > > + continue; > > + } > > + > > + if (sg) > > + sg_page_sizes |= sg->length; > > + > > + sg = sg ? __sg_next(sg) : st->sgl; > > + sg_dma_address(sg) = addr; > > + sg_dma_len(sg) = PAGE_SIZE; > > This still can't be like this - assigning pfn to 'dma_address' is > fundamentally wrong. > > Whatever explanation you had, this needs to be fixed up first before we get > to this patch. > The pfn is converted into a device address which goes into sg_dma_address. Ok, let me think about what else we can do here.If you combine this with the other function and make it so only DEVICE_PRIVATE pages get converted toa dma_address with out dma_map, then that would make sense.
Ok thanks, will do that.
> > +static int > > +i915_svm_invalidate_range_start(struct mmu_notifier *mn, > > + const struct mmu_notifier_range *update) > > +{ > > + struct i915_svm *svm = container_of(mn, struct i915_svm, notifier); > > + unsigned long length = update->end - update->start; > > + > > + DRM_DEBUG_DRIVER("start 0x%lx length 0x%lx\n", update->start, length); > > + if (!mmu_notifier_range_blockable(update)) > > + return -EAGAIN; > > + > > + i915_gem_vm_unbind_svm_buffer(svm->vm, update->start, length); > > + return 0; > > +} > > I still think you should strive for a better design than putting a > notifier across the entire address space.. > Yah, thought it could be later optimization. If I think about it, it has be be a new user API to set the range, or an intermediate data structure for tracking the bound ranges. Will look into it.Well, there are lots of options. Like I said, implicit ODP uses a level of the device page table to attach the notifier. There are many performance trade offs here, it depends what works best for your work load I suppose. But usually the fault path is the fast thing, so I would think to avoid registering mmu_intervals on it and accept the higher probability of collisions.
Ok thanks, yah, solution should tune for the performant path. Will look into it. Thanks, Niranjana
Jason
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