On at 2018-11-05 15:51 +0100, Tom Ehlert wrote:
>> the FreeDOS kernel is seriously slower then MSDOS when doing
>> larger copy/xcopy operations.
>
>> the cause: the disk I/O code avoids transfers that cross a 64K
>> boundary, and splits these transfers into 3 (smaller) transfers.
>
>> this was needed for floppy controllers in the 1980's, but is certainly
>> not necessary for harddisks after the IBM XT.
>
>
>> just skip
>
>
>> /* avoid overflowing 64K DMA boundary */
>> count = DMA_max_transfer(buffer, totaltodo);
>
>> for harddisks, and everything should be *much* faster (at least on
>> rotating media in a non-emulated machine)
>
> investigating in this a bit more, the 64K boundary was/is a problem
> with ISA DMA, used only for floppies (and sometimes serial/parallel
> ports), but is no problem for UDMA.
>
> skipping this test for drives with 0x80 set should be save, and result
> in a significant speedup of large disk transfers.
Another possibility is to depend on the error code (ah = 09h, RBIL lists
this as "data boundary error (attempted DMA across 64K boundary or >80h
sectors)") and retry the calls to avoid 64 KiB boundaries only then.
I've had success with that when loading from an actual diskette drive;
the error is properly reported and handled this way.
Regards,
ecm
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