On Thu, Jan 27, 2022 at 12:51 PM Chaitanya Kulkarni <chaitanyak@xxxxxxxxxx> wrote: > > Hi, > > * Background :- > ----------------------------------------------------------------------- > > Copy offload is a feature that allows file-systems or storage devices > to be instructed to copy files/logical blocks without requiring > involvement of the local CPU. > > With reference to the RISC-V summit keynote [1] single threaded > performance is limiting due to Denard scaling and multi-threaded > performance is slowing down due Moore's law limitations. With the rise > of SNIA Computation Technical Storage Working Group (TWG) [2], > offloading computations to the device or over the fabrics is becoming > popular as there are several solutions available [2]. One of the common > operation which is popular in the kernel and is not merged yet is Copy > offload over the fabrics or on to the device. > > * Problem :- > ----------------------------------------------------------------------- > > The original work which is done by Martin is present here [3]. The > latest work which is posted by Mikulas [4] is not merged yet. These two > approaches are totally different from each other. Several storage > vendors discourage mixing copy offload requests with regular READ/WRITE > I/O. Also, the fact that the operation fails if a copy request ever > needs to be split as it traverses the stack it has the unfortunate > side-effect of preventing copy offload from working in pretty much > every common deployment configuration out there. > > * Current state of the work :- > ----------------------------------------------------------------------- > > With [3] being hard to handle arbitrary DM/MD stacking without > splitting the command in two, one for copying IN and one for copying > OUT. Which is then demonstrated by the [4] why [3] it is not a suitable > candidate. Also, with [4] there is an unresolved problem with the > two-command approach about how to handle changes to the DM layout > between an IN and OUT operations. > > We have conducted a call with interested people late last year since > lack of LSFMMM and we would like to share the details with broader > community members. I'm keen on this topic and would like to join the F2F discussion. The Novmber call did establish some consensus on requirements. Planning to have a round or two of code-discussions soon. Thanks, -- Kanchan
