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x86: A fast way to check capabilities of the current cpu

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Add this_cpu_has() which determines if the current cpu has a certain
ability using a segment prefix and a bit test operation.

For that we need to add bit operations to x86s percpu.h.

Many uses of cpu_has use a pointer passed to a function to determine
the current flags. That is no longer necessary after this patch.

However, this patch only converts the straightforward cases where
cpu_has is used with this_cpu_ptr. The rest is work for later.

-tj: Rolled up patch to add x86_ prefix and use percpu_read() instead
     of percpu_read_stable().

Signed-off-by: Christoph Lameter <cl@linux.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Christoph Lameter
2011-03-12 12:50:10 +01:00
committed by Tejun Heo
parent 89078d572e
commit 349c004e3d
5 changed files with 41 additions and 9 deletions
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27
arch/x86/include/asm/percpu.h
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@@ -542,6 +542,33 @@ do { \
old__; \
})
static __always_inline int x86_this_cpu_constant_test_bit(unsigned int nr,
const unsigned long __percpu *addr)
{
unsigned long __percpu *a = (unsigned long *)addr + nr / BITS_PER_LONG;
return ((1UL << (nr % BITS_PER_LONG)) & percpu_read(*a)) != 0;
}
static inline int x86_this_cpu_variable_test_bit(int nr,
const unsigned long __percpu *addr)
{
int oldbit;
asm volatile("bt "__percpu_arg(2)",%1\n\t"
"sbb %0,%0"
: "=r" (oldbit)
: "m" (*(unsigned long *)addr), "Ir" (nr));
return oldbit;
}
#define x86_this_cpu_test_bit(nr, addr) \
(__builtin_constant_p((nr)) \
? x86_this_cpu_constant_test_bit((nr), (addr)) \
: x86_this_cpu_variable_test_bit((nr), (addr)))
#include <asm-generic/percpu.h>
/* We can use this directly for local CPU (faster). */