Re: rfc/rft: use r10 as current on x86-64

From: Brian Gerst (bgerst_at_didntduck.org)
Date: 11/22/05

  • Next message: Gerd Knorr: "[patch] SMP alternatives" 
    Date:	Tue, 22 Nov 2005 12:46:38 -0500
To: Andi Kleen <ak@suse.de>

    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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