On 17/07/17 12:57, 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?
Sorry, I'm not familiar with OpenCL/GPU drivers. It is up to them to decide where to allocate memory for clSVMAlloc. My SMMU work would deal with fine-grained *system* SVM, the kind that can be obtained from malloc and doesn't require a call to clSVMAlloc. Hopefully others on this list or linux-mm might be able to help you. Thanks, Jean > Thanks > Yisheng Xie > >> HMM deals with physical >> storage. If I understand correctly, HMM allows to transparently use device >> RAM from userspace applications. So upon an I/O page fault, the mm >> subsystem will migrate data from system memory into device RAM. It would >> differ from "pure" SVM in that you would use different page directories on >> IOMMU and MMU sides, and synchronize them using MMU notifiers. But please >> don't take this at face value, I haven't had time to look into HMM yet. >> >> Thanks, >> Jean >> >> . >> >
