On 5/29/24 15:17, Nitesh Shetty wrote: > On 24/05/24 01:33PM, Bart Van Assche wrote: >> On 5/20/24 03:20, Nitesh Shetty wrote: >>> We add two new opcode REQ_OP_COPY_DST, REQ_OP_COPY_SRC. >>> Since copy is a composite operation involving src and dst sectors/lba, >>> each needs to be represented by a separate bio to make it compatible >>> with device mapper. >>> We expect caller to take a plug and send bio with destination information, >>> followed by bio with source information. >>> Once the dst bio arrives we form a request and wait for source >>> bio. Upon arrival of source bio we merge these two bio's and send >>> corresponding request down to device driver. >>> Merging non copy offload bio is avoided by checking for copy specific >>> opcodes in merge function. >> >> In this patch I don't see any changes for blk_attempt_bio_merge(). Does >> this mean that combining REQ_OP_COPY_DST and REQ_OP_COPY_SRC will never >> happen if the QUEUE_FLAG_NOMERGES request queue flag has been set? >> > Yes, in this case copy won't work, as both src and dst bio reach driver > as part of separate requests. > We will add this as part of documentation. So that means that 2 major SAS HBAs which set this flag (megaraid and mpt3sas) will not get support for copy offload ? Not ideal, by far. -- Damien Le Moal Western Digital Research
