Andi Kleen wrote:
I tried that once on x86-64, but it wasn't possible because the linker
is missing the right relocations. It has something on the first look similar
for __thread data in user space, but it wasn't usable for the kernel.
The other difficulty is that you can't take the addresses of things in
the pda and pass them around, which happens a lot. It would be another
matter if you could add an attribute to a pointer which told gcc "always
use a %gs override for indirecting through this pointer", though that
would still require some type qualifier on any pointer which holds the
value.
(Hm, it would be interesting to see if we could possibly use the code
generated by gcc for TLS variables...)
Even with a single indirection it is still far more efficient than a
array lookup.
Yes. Even in the Xen case it will be useful to have a pointer to the
vcpu structure, at least until Xen can be convinced to put the vcpu
structure in the PDA itself.
J
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