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x86: vdso: pvclock gettime support

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Improve performance of time system calls when using Linux pvclock,
by reading time info from fixmap visible copy of pvclock data.

Originally from Jeremy Fitzhardinge.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Marcelo Tosatti 2012-11-27 23:28:57 -02:00
parent 3dc4f7cfb7
commit 51c19b4f59
3 changed files with 101 additions and 11 deletions
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20
arch/x86/include/asm/vsyscall.h
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@ -33,6 +33,26 @@ extern void map_vsyscall(void);
*/
extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
#ifdef CONFIG_X86_64
#define VGETCPU_CPU_MASK 0xfff
static inline unsigned int __getcpu(void)
{
unsigned int p;
if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
native_read_tscp(&p);
} else {
/* Load per CPU data from GDT */
asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
}
return p;
}
#endif /* CONFIG_X86_64 */
#endif /* __KERNEL__ */
#endif /* _ASM_X86_VSYSCALL_H */