Re: bigphysarea support in 2.2.19 and 2.4.0 kernels

Albert D. Cahalan
2000-12-24T08:46:51Z

Jes Sorensen writes:
> Albert D Cahalan <acahalan@cs.uml.edu> writes:

[about using huge physical allocations for number crunching]

>> 2. Programming a DMA controller with multiple addresses isn't
>> as fast as programming it with one.
>
> LOL
>
> Consider that allocating the larger block of memory is going
> to take a lot longer than it will take for the DMA engine to
> read the scatter/gather table entries and fetch a new address
> word now and then.

Say it takes a whole minute to allocate the memory. It wouldn't
of course, because you'd allocate memory at boot, but anyway...
Then the app runs, using that memory, for a multi-hour surgery.
The allocation happens once; the inter-node DMA transfers occur
dozens or hundreds of times per second.