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    SubjectRe: Linux and real device drivers
    >>>>> "Momchil" == Momchil Velikov <> writes:

    Momchil> Alan Cox wrote:
    >> There is the jump/return overhead. There is the stack management
    >> overhead There is an extra cache line touched.

    Momchil> Ok, folks, I think we are talking about "udi_pio_trans" call
    Momchil> (in UDI Physical I/O Specification) and this call is surely
    Momchil> not meant to perform a single I/O port or MMIO
    Momchil> read/write. Instead the UDI implementation executes a large
    Momchil> transaction including many reads, writes, arithmetic
    Momchil> operations, branches, etc. Now, the overhead is by no means
    Momchil> in the call, it's in interpreting the transaction description
    Momchil> and I'd say yes, it ought to be rather big.

    No, for Gigabit Ethernet I have to do some 5-10 read/writes per packet
    to PCI shared memory, however these are not all one large block and
    go to different places in the PCI shared mem area. Most of this will
    have to be done with multiple UDI calls, unless they came up with a
    scatter/gather type list for this .... yuck.


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