From e26a9e00afc482b971afcaef1db8c9034d4d6d7c Mon Sep 17 00:00:00 2001 From: Russell King Date: Tue, 25 Mar 2014 19:45:31 +0000 Subject: ARM: Better virt_to_page() handling virt_to_page() is incredibly inefficient when virt-to-phys patching is enabled. This is because we end up with this calculation: page = &mem_map[asm virt_to_phys(addr) >> 12 - __pv_phys_offset >> 12] in assembly. The asm virt_to_phys() is equivalent this this operation: addr - PAGE_OFFSET + __pv_phys_offset and we can see that because this is assembly, the compiler has no chance to optimise some of that away. This should reduce down to: page = &mem_map[(addr - PAGE_OFFSET) >> 12] for the common cases. Permit the compiler to make this optimisation by giving it more of the information it needs - do this by providing a virt_to_pfn() macro. Another issue which makes this more complex is that __pv_phys_offset is a 64-bit type on all platforms. This is needlessly wasteful - if we store the physical offset as a PFN, we can save a lot of work having to deal with 64-bit values, which sometimes ends up producing incredibly horrid code: a4c: e3009000 movw r9, #0 a4c: R_ARM_MOVW_ABS_NC __pv_phys_offset a50: e3409000 movt r9, #0 ; r9 = &__pv_phys_offset a50: R_ARM_MOVT_ABS __pv_phys_offset a54: e3002000 movw r2, #0 a54: R_ARM_MOVW_ABS_NC __pv_phys_offset a58: e3402000 movt r2, #0 ; r2 = &__pv_phys_offset a58: R_ARM_MOVT_ABS __pv_phys_offset a5c: e5999004 ldr r9, [r9, #4] ; r9 = high word of __pv_phys_offset a60: e3001000 movw r1, #0 a60: R_ARM_MOVW_ABS_NC mem_map a64: e592c000 ldr ip, [r2] ; ip = low word of __pv_phys_offset Reviewed-by: Nicolas Pitre Signed-off-by: Russell King --- arch/arm/kernel/armksyms.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/arm/kernel/armksyms.c') diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c index 85e664b..f7b450f 100644 --- a/arch/arm/kernel/armksyms.c +++ b/arch/arm/kernel/armksyms.c @@ -158,6 +158,6 @@ EXPORT_SYMBOL(__gnu_mcount_nc); #endif #ifdef CONFIG_ARM_PATCH_PHYS_VIRT -EXPORT_SYMBOL(__pv_phys_offset); +EXPORT_SYMBOL(__pv_phys_pfn_offset); EXPORT_SYMBOL(__pv_offset); #endif -- cgit v1.1