• Sagi Grimberg's avatar
    IB/iser: Support up to 8MB data transfer in a single command · df749cdc
    Sagi Grimberg authored
    iser support up to 512KB data transfer in a single scsi command.
    This means that larger IOs will split to different request. While
    iser can easily saturate FDR/EDR wires, some arrays are fine tuned
    for 1MB (or larger) IO sizes, hence add an option to support larger
    transfers (up to 8MB) if the device allows it.
    
    Given that a few target implementations don't support data transfers
    of more than 512KB by default and the fact that larger IO sizes require
    more resources, we introduce a module parameter to determine the
    maximum number of 512B sectors in a single scsi command.
    Users that are interested in larger transfers can change this value given
    that the target supports larger transfers.
    
    At the moment, iser works in 4K pages granularity, In a later stage
    we will get it to work with system page size instead.
    
    IO operations that consists of N pages will need a page vector
    of size N+1 in case the first SG element contains an offset. Given
    that some devices allocates memory regions in powers of 2, this
    means that allocating a region with N+1 pages, will result in
    region resources allocation of the next power of 2. Since we don't
    want that to happen, in case we are in the limit of IO size supported
    and the first SG element has an offset, we align the SG list using a
    bounce buffer (which is OK given that this is not likely to happen a lot).
    Signed-off-by: default avatarSagi Grimberg <sagig@mellanox.com>
    Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
    df749cdc
iscsi_iser.h 21.5 KB