Hi Jérôme and Jean-Philippe , Get it, thanks for all of your detail explain.
Thanks Yisheng Xie On 2017/7/17 22:27, Jerome Glisse wrote: > On Mon, Jul 17, 2017 at 07:57:23PM +0800, Yisheng Xie wrote: >> Hi Jean-Philippe， >> >> On 2017/6/12 19:37, Jean-Philippe Brucker wrote: >>> Hello, >>> >>> On 10/06/17 05:06, Wuzongyong (Cordius Wu, Euler Dept) wrote: >>>> Hi, >>>> >>>> Could someone explain differences and relations between the SVM(Shared >>>> Virtual Memory, by Intel), HSA(Heterogeneous System Architecture, by AMD), >>>> HMM(Heterogeneous Memory Management, by Glisse) and UM(Unified Memory, by >>>> NVIDIA) ? Are these in the substitutional relation? >>>> >>>> As I understand it, these aim to solve the same thing, sharing pointers >>>> between CPU and GPU(implement with ATS/PASID/PRI/IOMMU support). So far, >>>> SVM and HSA can only be used by integrated gpu. And, Intel declare that >>>> the root ports doesn’t not have the required TLP prefix support, resulting >>>> that SVM can’t be used by discrete devices. So could someone tell me the >>>> required TLP prefix means what specifically?> >>>> With HMM, we can use allocator like malloc to manage host and device >>>> memory. Does this mean that there is no need to use SVM and HSA with HMM, >>>> or HMM is the basis of SVM and HAS to implement Fine-Grained system SVM >>>> defined in the opencl spec? >>> >>> I can't provide an exhaustive answer, but I have done some work on SVM. >>> Take it with a grain of salt though, I am not an expert. >>> >>> * HSA is an architecture that provides a common programming model for CPUs >>> and accelerators (GPGPUs etc). It does have SVM requirement (I/O page >>> faults, PASID and compatible address spaces), though it's only a small >>> part of it. >>> >>> * Similarly, OpenCL provides an API for dealing with accelerators. OpenCL >>> 2.0 introduced the concept of Fine-Grained System SVM, which allows to >>> pass userspace pointers to devices. It is just one flavor of SVM, they >>> also have coarse-grained and non-system. But they might have coined the >>> name, and I believe that in the context of Linux IOMMU, when we talk about >>> "SVM" it is OpenCL's fine-grained system SVM. >>> [...] >>> >>> While SVM is only about virtual address space, >> As you mentioned, SVM is only about virtual address space, I'd like to know >> how to >> manage the physical address especially about device's RAM, before HMM? >> >> When OpenCL alloc a SVM pointer like: >> void* p = clSVMAlloc ( >> context, // an OpenCL context where this buffer is available >> CL_MEM_READ_WRITE | CL_MEM_SVM_FINE_GRAIN_BUFFER, >> size, // amount of memory to allocate (in bytes) >> 0 // alignment in bytes (0 means default) >> ); >> >> where this RAM come from， device RAM or host RAM? >> > > For SVM using ATS/PASID with FINE_GRAIN your allocation can only > be inside the system memory (host RAM). You need a special system > bus like CAPI or CCIX which both are step further than ATS/PASID > to be able to allow fine grain to use device memory. > > However that is where HMM can be usefull as HMM is a software > solution to this problem. So with HMM and a device that can work > with HMM, you can get fine grain allocation to also use device > memory however any CPU access will happen in host RAM. > > Jérôme > > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
