diff options
| author | Russell King <rmk+kernel@arm.linux.org.uk> | 2014-03-25 19:45:31 +0000 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2014-04-03 22:46:34 +0100 |
| commit | e26a9e00afc482b971afcaef1db8c9034d4d6d7c (patch) | |
| tree | 6ed907fccdafda9a6656794db0543692f7e5d46f /arch/arm/kernel/armksyms.c | |
| parent | 83b3f64d46d1d9bf1e0be1d16f805ccdd52d31c6 (diff) | |
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 <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel/armksyms.c')
| -rw-r--r-- | arch/arm/kernel/armksyms.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c index 85e664b6a5f1..f7b450f97e68 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 |