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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
parent 54413927f0
commit 464d1a78fb
17 changed files with 99 additions and 103 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
arch/i386/kernel/process.c
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@ -308,8 +308,8 @@ void show_regs(struct pt_regs * regs)
regs->eax,regs->ebx,regs->ecx,regs->edx);
printk("ESI: %08lx EDI: %08lx EBP: %08lx",
regs->esi, regs->edi, regs->ebp);
printk(" DS: %04x ES: %04x GS: %04x\n",
0xffff & regs->xds,0xffff & regs->xes, 0xffff & regs->xgs);
printk(" DS: %04x ES: %04x FS: %04x\n",
0xffff & regs->xds,0xffff & regs->xes, 0xffff & regs->xfs);
cr0 = read_cr0();
cr2 = read_cr2();
@ -340,7 +340,7 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
regs.xds = __USER_DS;
regs.xes = __USER_DS;
regs.xgs = __KERNEL_PDA;
regs.xfs = __KERNEL_PDA;
regs.orig_eax = -1;
regs.eip = (unsigned long) kernel_thread_helper;
regs.xcs = __KERNEL_CS | get_kernel_rpl();
@ -425,7 +425,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
p->thread.eip = (unsigned long) ret_from_fork;
savesegment(fs,p->thread.fs);
savesegment(gs,p->thread.gs);
tsk = current;
if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
@ -501,8 +501,8 @@ void dump_thread(struct pt_regs * regs, struct user * dump)
dump->regs.eax = regs->eax;
dump->regs.ds = regs->xds;
dump->regs.es = regs->xes;
savesegment(fs,dump->regs.fs);
dump->regs.gs = regs->xgs;
dump->regs.fs = regs->xfs;
savesegment(gs,dump->regs.gs);
dump->regs.orig_eax = regs->orig_eax;
dump->regs.eip = regs->eip;
dump->regs.cs = regs->xcs;
@ -653,7 +653,7 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
load_esp0(tss, next);
/*
* Save away %fs. No need to save %gs, as it was saved on the
* Save away %gs. No need to save %fs, as it was saved on the
* stack on entry. No need to save %es and %ds, as those are
* always kernel segments while inside the kernel. Doing this
* before setting the new TLS descriptors avoids the situation
@ -662,7 +662,7 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
* used %fs or %gs (it does not today), or if the kernel is
* running inside of a hypervisor layer.
*/
savesegment(fs, prev->fs);
savesegment(gs, prev->gs);
/*
* Load the per-thread Thread-Local Storage descriptor.
@ -670,12 +670,10 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
load_TLS(next, cpu);
/*
* Restore %fs if needed.
*
* Glibc normally makes %fs be zero.
* Restore %gs if needed (which is common)
*/
if (unlikely(prev->fs | next->fs))
loadsegment(fs, next->fs);
if (prev->gs | next->gs)
loadsegment(gs, next->gs);
write_pda(pcurrent, next_p);