From 464d1a78fbf8cf6c7fd970e7b3e2db50a320ce28 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Tue, 13 Feb 2007 13:26:20 +0100 Subject: [PATCH] i386: Convert i386 PDA code to use %fs 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 Signed-off-by: Andi Kleen Cc: Ian Campbell Acked-by: Ingo Molnar Acked-by: Zachary Amsden Cc: Eric Dumazet Signed-off-by: Frederik Deweerdt Signed-off-by: Andrew Morton --- arch/i386/kernel/cpu/common.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'arch/i386/kernel/cpu/common.c') diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c index 8a8bbdaaf38..dcbbd0a8bfc 100644 --- a/arch/i386/kernel/cpu/common.c +++ b/arch/i386/kernel/cpu/common.c @@ -605,7 +605,7 @@ void __init early_cpu_init(void) struct pt_regs * __devinit idle_regs(struct pt_regs *regs) { memset(regs, 0, sizeof(struct pt_regs)); - regs->xgs = __KERNEL_PDA; + regs->xfs = __KERNEL_PDA; return regs; } @@ -662,12 +662,12 @@ struct i386_pda boot_pda = { .pcurrent = &init_task, }; -static inline void set_kernel_gs(void) +static inline void set_kernel_fs(void) { - /* Set %gs for this CPU's PDA. Memory clobber is to create a + /* Set %fs for this CPU's PDA. Memory clobber is to create a barrier with respect to any PDA operations, so the compiler doesn't move any before here. */ - asm volatile ("mov %0, %%gs" : : "r" (__KERNEL_PDA) : "memory"); + asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_PDA) : "memory"); } /* Initialize the CPU's GDT and PDA. The boot CPU does this for @@ -718,7 +718,7 @@ void __cpuinit cpu_set_gdt(int cpu) the boot CPU, this will transition from the boot gdt+pda to the real ones). */ load_gdt(cpu_gdt_descr); - set_kernel_gs(); + set_kernel_fs(); } /* Common CPU init for both boot and secondary CPUs */ @@ -764,8 +764,8 @@ static void __cpuinit _cpu_init(int cpu, struct task_struct *curr) __set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss); #endif - /* Clear %fs. */ - asm volatile ("mov %0, %%fs" : : "r" (0)); + /* Clear %gs. */ + asm volatile ("mov %0, %%gs" : : "r" (0)); /* Clear all 6 debug registers: */ set_debugreg(0, 0); -- cgit v1.2.3