Hi Jeremy,
a last minute request for the new kernel release:
In context of the patch for significant I/O speed improvements
by only splitting transfers around DMA boundaries for drives
where that actually is needed, based on the int 13.48 flags,
please add a config sys option to override the int 13.48 answer
into either "always avoid DMA boundaries" or "always assume DMA
boundaries are no problem" for all fixed disks (0x80 and up).
Background: MS DOS, predating the int 13.4x extensions, probably
defaults to never avoiding DMA boundaries for fixed disks and
always avoiding them for floppy. So the config sys flag can give
us MS DOS speed and behavior even when using BIOSes which fail
to properly report their ability to transparently handle any DMA
boundary issues. We would needlessly lose I/O speed otherwise.
The other option, always avoiding DMA boundaries, would allow
the user to switch back to old FreeDOS behaviour, for example
for benchmark comparisons or for cases where the BIOS claims
to be DMA boundary safe, but actually messes up handling there.
Thanks :-) As said, the ability to either avoid or not avoid DMA
boundaries would make a big difference for I/O speed. I think it
was Tom who proposed the patch which made us int 13.48 aware :-)
Regards, Eric
PS: I think it is NOT necessary to have similar options for
individual drive numbers, because any mismatch between the
reported and actual abilities will usually affect all disks
of the same BIOS and having 2+ broken disk BIOSes is uncommon.
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