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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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