On 27.01.2022 07:14, Chaitanya Kulkarni 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.
Chaitanya, I would also like to join the F2F conversation as a follow up of the virtual one last year. We will have a first version of the patches posted in the next few weeks. This will hopefully serve as a good first step. Adding Kanchan to thread too. Javier
