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SubjectRe: rfc/rft: use r10 as current on x86-64
Andi Kleen wrote:
> On Tue, Nov 22, 2005 at 11:52:04AM -0500, Benjamin LaHaise wrote:
>> Hello Andi et al,
>>
>> The patch below converts x86-64 to use r10 as the current pointer instead
>> of gs:pcurrent. This results in a ~34KB savings in the code segment of
>> the kernel. I've tested this with running a few regular applications,
>> plus a few 32 bit binaries. If this patch is interesting, it probably
>> makes sense to merge the thread info structure into the task_struct so
>> that the assembly bits for syscall entry can be cleaned up. Comments?
>
> I think you could get most of the benefit by just dropping
> the volatile and "memory" from read_pda(). With that gcc would
> usually CSE current into a register and it would would work essentially
> the same way with only minor more .text overhead, but r10 would be still
> available.

It seems that GCC is reluctant to use the extended registers anyways
because of the rex prefix, so I don't think dedicating r10 to current
will cause that many problems.

--
Brian Gerst
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