timer: Replace timer base by a cpu index

Instead of storing a pointer to the per cpu tvec_base we can simply
cache a CPU index in the timer_list and use that to get hold of the
correct per cpu tvec_base. This is only used in lock_timer_base() and
the slightly larger code is peanuts versus the spinlock operation and
the d-cache foot print of the timer wheel.

Aside of that this allows to get rid of following nuisances:

 - boot_tvec_base

   That statically allocated 4k bss data is just kept around so the
   timer has a home when it gets statically initialized. It serves no
   other purpose.

   With the CPU index we assign the timer to CPU0 at static
   initialization time and therefor can avoid the whole boot_tvec_base
   dance.  That also simplifies the init code, which just can use the
   per cpu base.

   Before:
     text	   data	    bss	    dec	    hex	filename
    17491	   9201	   4160	  30852	   7884	../build/kernel/time/timer.o
   After:
     text	   data	    bss	    dec	    hex	filename
    17440	   9193	      0	  26633	   6809	../build/kernel/time/timer.o

 - Overloading the base pointer with various flags

   The CPU index has enough space to hold the flags (deferrable,
   irqsafe) so we can get rid of the extra masking and bit fiddling
   with the base pointer.

As a benefit we reduce the size of struct timer_list on 64 bit
machines. 4 - 8 bytes, a size reduction up to 15% per struct timer_list,
which is a real win as we have tons of them embedded in other structs.

This changes also the newly added deferrable printout of the timer
start trace point to capture and print all timer->flags, which allows
us to decode the target cpu of the timer as well.

We might have used bitfields for this, but that would change the
static initializers and the init function for no value to accomodate
big endian bitfields.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Joonwoo Park <joonwoop@codeaurora.org>
Cc: Wenbo Wang <wenbo.wang@memblaze.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Badhri Jagan Sridharan <Badhri@google.com>
Link: http://lkml.kernel.org/r/20150526224511.950084301@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 7 deletions

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index d7abef1fe6e0..073b9ac245ba 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -45,16 +45,16 @@ TRACE_EVENT(timer_start,
 
 	TP_PROTO(struct timer_list *timer,
 		unsigned long expires,
-		unsigned int deferrable),
+		unsigned int flags),
 
-	TP_ARGS(timer, expires, deferrable),
+	TP_ARGS(timer, expires, flags),
 
 	TP_STRUCT__entry(
 		__field( void *,	timer		)
 		__field( void *,	function	)
 		__field( unsigned long,	expires		)
 		__field( unsigned long,	now		)
-		__field( unsigned int,	deferrable	)
+		__field( unsigned int,	flags		)
 	),
 
 	TP_fast_assign(
@@ -62,13 +62,12 @@ TRACE_EVENT(timer_start,
 		__entry->function	= timer->function;
 		__entry->expires	= expires;
 		__entry->now		= jiffies;
-		__entry->deferrable     = deferrable;
+		__entry->flags		= flags;
 	),
 
-	TP_printk("timer=%p function=%pf expires=%lu [timeout=%ld] defer=%c",
+	TP_printk("timer=%p function=%pf expires=%lu [timeout=%ld] flags=0x%08x",
 		  __entry->timer, __entry->function, __entry->expires,
-		  (long)__entry->expires - __entry->now,
-		  __entry->deferrable > 0 ? 'y':'n')
+		  (long)__entry->expires - __entry->now, __entry->flags)
 );
 
 /**