perf/x86: Add a native_perf_sched_clock_from_tsc()

PEBSv3 has a raw TSC time stamp in its memory buffer that
later needs to to be converted to perf_clock.

Add a native_sched_clock_from_tsc() that works the same
as native_sched_clock(), but starts with an already given
TSC value.

Paravirt is ignored, it will just get the native clock.
But there isn't a para virtualized PEBS anyway.

Signed-off-by: Andi Kleen <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: Andi Kleen

arch/x86/include/asm/tsc.h

@@ -51,6 +51,7 @@ extern int unsynchronized_tsc(void);
 extern int check_tsc_unstable(void);
 extern int check_tsc_disabled(void);
 extern unsigned long native_calibrate_tsc(void);
+extern unsigned long long native_sched_clock_from_tsc(u64 tsc);
 
 extern int tsc_clocksource_reliable;
 

arch/x86/kernel/tsc.c

@@ -296,6 +296,14 @@ u64 native_sched_clock(void)
 	return cycles_2_ns(tsc_now);
 }
 
+/*
+ * Generate a sched_clock if you already have a TSC value.
+ */
+u64 native_sched_clock_from_tsc(u64 tsc)
+{
+	return cycles_2_ns(tsc);
+}
+
 /* We need to define a real function for sched_clock, to override the
    weak default version */
 #ifdef CONFIG_PARAVIRT