On Mon, Feb 06, 2023 at 10:26:55AM -0800, Bart Van Assche wrote: > On 2/6/23 07:00, Ming Lei wrote: > > 4) DMA > > - DMA requires physical memory address, UBLK driver actually has > > block request pages, so can we export request SG list(each segment > > physical address, offset, len) into userspace? If the max_segments > > limit is not too big(<=64), the needed buffer for holding SG list > > can be small enough. > > > > - small amount of physical memory for using as DMA descriptor can be > > pre-allocated from userspace, and ask kernel to pin pages, then still > > return physical address to userspace for programming DMA > > > > - this way is still zero copy > > Would it be possible to use vfio in such a way that zero-copy > functionality is achieved? I'm concerned about the code duplication that > would result if a new interface similar to vfio is introduced. Here I meant we can export physical address of request sg from /dev/ublkb* to userspace, which can program the DMA controller using exported physical address. With this way, the userspace driver can submit IO without entering kernel, then with high performance. This should how SPDK/nvme-pci[1] is implemented, but SPDK allocates hugepage for getting its physical address. [1] https://spdk.io/doc/memory.html Thanks, Ming
