x86: vdso: pvclock gettime support

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>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index eaea1d31f753..80f80955cfd8 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -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 */