tracing: Unify the "boot" and "mono" tracing clocks

Unify the "boot" and "mono" tracing clocks and document the new behaviour.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Dmitry Torokhov <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Kevin Easton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mark Salyzyn <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Steven Rostedt <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Documentation/trace/ftrace.txt

@@ -449,17 +449,9 @@ of ftrace. Here is a list of some of the key files:
 		which is montonic but is not subject to any rate adjustments
 		and ticks at the same rate as the hardware clocksource.
 
-	  boot: This is the boot clock (CLOCK_BOOTTIME) and is based on the
-		fast monotonic clock, but also accounts for time spent in
-		suspend. Since the clock access is designed for use in
-		tracing in the suspend path, some side effects are possible
-		if clock is accessed after the suspend time is accounted before
-		the fast mono clock is updated. In this case, the clock update
-		appears to happen slightly sooner than it normally would have.
-		Also on 32-bit systems, it's possible that the 64-bit boot offset
-		sees a partial update. These effects are rare and post
-		processing should be able to handle them. See comments in the
-		ktime_get_boot_fast_ns() function for more information.
+	  boot: Same as mono. Used to be a separate clock which accounted
+	  	for the time spent in suspend while CLOCK_MONOTONIC did
+		not.
 
 	To set a clock, simply echo the clock name into this file.
 

include/linux/timekeeping.h

@@ -113,12 +113,6 @@ extern u64 ktime_get_mono_fast_ns(void);
 extern u64 ktime_get_raw_fast_ns(void);
 extern u64 ktime_get_real_fast_ns(void);
 
-/* Clock BOOTTIME compatibility wrappers */
-static inline u64 ktime_get_boot_fast_ns(void)
-{
-	return ktime_get_mono_fast_ns();
-}
-
 /*
  * timespec64 interfaces utilizing the ktime based ones
  */

kernel/trace/trace.c

@@ -1164,7 +1164,7 @@ static struct {
 	{ trace_clock,			"perf",		1 },
 	{ ktime_get_mono_fast_ns,	"mono",		1 },
 	{ ktime_get_raw_fast_ns,	"mono_raw",	1 },
-	{ ktime_get_boot_fast_ns,	"boot",		1 },
+	{ ktime_get_mono_fast_ns,	"boot",		1 },
 	ARCH_TRACE_CLOCKS
 };