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[PATCH] i386: Convert i386 PDA code to use %fs

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Convert the PDA code to use %fs rather than %gs as the segment for
per-processor data.  This is because some processors show a small but
measurable performance gain for reloading a NULL segment selector (as %fs
generally is in user-space) versus a non-NULL one (as %gs generally is).

On modern processors the difference is very small, perhaps undetectable.
Some old AMD "K6 3D+" processors are noticably slower when %fs is used
rather than %gs; I have no idea why this might be, but I think they're
sufficiently rare that it doesn't matter much.

This patch also fixes the math emulator, which had not been adjusted to
match the changed struct pt_regs.

[frederik.deweerdt@gmail.com: fixit with gdb]
[mingo@elte.hu: Fix KVM too]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Ian Campbell <Ian.Campbell@XenSource.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Zachary Amsden <zach@vmware.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
This commit is contained in:
Jeremy Fitzhardinge 2007-02-13 13:26:20 +01:00 • committed by Andi Kleen
commit 464d1a78fb
17 changed files with 99 additions and 103 deletions
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6
include/asm-i386/processor.h
View file

@ -424,7 +424,7 @@ struct thread_struct {
.vm86_info = NULL, \
.sysenter_cs = __KERNEL_CS, \
.io_bitmap_ptr = NULL, \
.gs = __KERNEL_PDA, \
.fs = __KERNEL_PDA, \
}
/*
@ -442,8 +442,8 @@ struct thread_struct {
}
#define start_thread(regs, new_eip, new_esp) do { \
__asm__("movl %0,%%fs": :"r" (0)); \
regs->xgs = 0; \
__asm__("movl %0,%%gs": :"r" (0)); \
regs->xfs = 0; \
set_fs(USER_DS); \
regs->xds = __USER_DS; \
regs->xes = __USER_DS; \