On Thu, Apr 06, 2017 at 06:46:49PM +0800, Haozhong Zhang wrote: > On 04/06/17 11:24 +0100, Stefan Hajnoczi wrote: > > On Fri, Mar 31, 2017 at 04:41:44PM +0800, Haozhong Zhang wrote: > > > If option 'reserved-size=RSVD' is present, QEMU will reserve an > > > address range of size 'RSVD' after the ending address of pc-dimm > > > device. > > > > > > For the following example, > > > -object memory-backend-file,id=mem0,size=4G,... > > > -device nvdimm,id=dimm0,memdev=mem0,reserved-size=4K,... > > > > "reserved-size" is not a clear name. I suggest calling the property > > "num-flush-hints" (default 0). QEMU can calculate the actual size in > > bytes. > > > > -device nvdimm,num-flush-hints=1 > > > > QEMU will use one flush hint and reserve enough space (e.g. 1 page) for > > the MMIO region. > > > > Each flush hint can be as small as one cache line size which is also > the size used in this patch series. > > We need to calculate the size of all flush hints in pc_dimm_memory_plug(), > because when building the flush hint address structure we need to know > the address of flush hints. > > IIUC, pc_dimm_memory_plug() is not specific to x86, so it's better > take a general way to get the vcpu cache line size in pc_dimm_memory_plug(), > which seemingly lacks in QEMU (though I believe it should be doable). > > To make things simple, I leave the size decision to users, and check > whether it's large enough when building the flush hint address > structures in patch 4.
Do you see my concern that "reserved-size" is not a good property? * How does the user choose a sensible value? * Why is it called "reserved-size" instead of "flush-hints-size"? Stefan
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