On Sun, 18 Oct 1998, David S. Miller wrote:
> I think that using a bitwise flag (use_timeout) could eventually
> also improve performance because when the timeout expire we don' t
> need to set to 0 a 64 bit memory area on 64bit arch. I am not 100%
> sure though ;-).
>
>On most RISC machines, bitfield extract/store is implemented as word
^^^^
I guess that there are not asm instruction for bitwise memory accesses.
Word means 32 or 64 bit (->timeout is a 64 bit memory area)? I have no
cross compier to check the output asm here.
Correct, and in fact on the Alpha you cannot even load a half-word
(16-bits) or (8-bit) quantity by itself into a register unless you
have a very recent Alpha cpu.
The size of this "word" is whatever the architecture natural word size
is, 64-bits on sparc64/alpha and 32-bit on most others.
>memory operations with the bit twiddle in the register. This is
>actually specified by the ABI, sparc64 and alpha do this for example.
ABI ??
"Application Binary Interface" they describe things other than the ELF
object file format there you know :-) They tell how bitfields are
layed out in structures and suggested ways to load/store/modify them
in assembler etc.
Later,
David S. Miller
davem@dm.cobaltmicro.com
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