Hi everyone!
I'm just asking myself at what limit I should put on the SUB-Block area.
SUB-Block area contains additional information to devices like e.g. device-name (for
PnP and USB), the
device proposals (Resource requirements) and extra information like for bridges and so
on.
One SUB-Block Allocation entry is 32 bytes and I thought about limiting to 32768 bytes
in total, which means
1024 SUB-Block segments (total limit 64MB, which is insane size).
The limit on devices is 8192 and this would make 8k SUB-Block space per device.
The problem with that limit is that I would need to allocate 2048 (!) GDT-selectors,
because I need to map the
space for Ring-0 *and* Ring-3 and that's the whole problem.
I think about limiting to 16 or 32MB, resulting in 2k or 4k SUB-Block average possible
size per device.
SUB-Block minimum size is 512 bytes and most of the time that should be enough. Often
devices do not even
need a SUB-Block at all.
What do you think? Even 512 GDT-selectors would be still a huge requirement, but there
is nothing to work
around this. Enlarging (which means allocating) is done run-time, which means it's
able to enlarge the area
during system run, so GCONFIG starts with one 64k segment for SUB-Blocks and one 64k
segment for
BASE-Blocks, but the GDT selectors need to get allocated at init time. (BASE-Blocks
may use up to 8
segments, which means 16 GDT-Selectors).
A practical example: My system currently has 27 BASE-Blocks (which means 27 devices),
all of those devices
have SUB-Block(s), but they are all below 512 bytes, which would mean around 15k
actual memory
requirement for the data, total actual detection area size is 4-5k (!!).
cu, Kiewitz
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