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
