forked from Minki/linux
4db7327194
We do binary patching of asm code using CPU features, which is a
one-time operation, done during early boot. However checks of CPU
features in C code are currently done at run time, even though the set
of CPU features can never change after boot.
We can optimise this by using jump labels to implement cpu_has_feature(),
meaning checks in C code are binary patched into a single nop or branch.
For a C sequence along the lines of:
if (cpu_has_feature(FOO))
return 2;
The generated code before is roughly:
ld r9,-27640(r2)
ld r9,0(r9)
lwz r9,32(r9)
cmpwi cr7,r9,0
bge cr7, 1f
li r3,2
blr
1: ...
After (true):
nop
li r3,2
blr
After (false):
b 1f
li r3,2
blr
1: ...
mpe: Rename MAX_CPU_FEATURES as we already have a #define with that
name, and define it simply as a constant, rather than doing tricks with
sizeof and NULL pointers. Rename the array to cpu_feature_keys. Use the
kconfig we added to guard it. Add BUILD_BUG_ON() if the feature is not a
compile time constant. Rewrite the change log.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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|---|---|---|
| .. | ||
| alloc.c | ||
| checksum_32.S | ||
| checksum_64.S | ||
| checksum_wrappers.c | ||
| code-patching.c | ||
| copy_32.S | ||
| copypage_64.S | ||
| copypage_power7.S | ||
| copyuser_64.S | ||
| copyuser_power7.S | ||
| crtsavres.S | ||
| div64.S | ||
| feature-fixups-test.S | ||
| feature-fixups.c | ||
| hweight_64.S | ||
| ldstfp.S | ||
| locks.c | ||
| Makefile | ||
| mem_64.S | ||
| memcmp_64.S | ||
| memcpy_64.S | ||
| memcpy_power7.S | ||
| ppc_ksyms.c | ||
| rheap.c | ||
| sstep.c | ||
| string_64.S | ||
| string.S | ||
| usercopy_64.c | ||
| vmx-helper.c | ||
| xor_vmx.c | ||