On Sun, 31 Dec 2000, Andi Kleen wrote:
>
> Sounds good. It could also be controlled by a CONFIG_SPACE_EFFICIENT for
> embedded systems, where you could trade a bit of CPU for less memory overhead
> even on systems where u8 is slow and atomicity doesn't come into play
> because it's UP anyways.
UP has nothing to do with it.
The alpha systems I remember this problem on were all SMP.
Imagine an architecture where you need to do a
load_32()
mask-and-insert-byte
store_32()
and imagine that an interrupt comes in:
load_32()
mask-and-insert-byte
* INTERRUPT *
load_32()
mask-and-insert-ANOTHER-byte
store_32()
interrupt return
store_32()
and notice how the value written by the interrupt is gone, gone, gone,
even though it was to a completely different byte.
Now, imagine that the first byte is the "age", and imagine that the thing
the interrupt tries to update is "flags".
Yes, you're screwed.
I don't think it's a good diea.
Linus
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This archive was generated by hypermail 2b29 : Sun Dec 31 2000 - 21:00:15 EST