[PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem)

Pass ticks to do_timer() and update_times(), and adjust x86_64 and s390
timer interrupt handler with this change.

Currently update_times() calculates ticks by "jiffies - wall_jiffies", but
callers of do_timer() should know how many ticks to update.  Passing ticks
get rid of this redundant calculation.  Also there are another redundancy
pointed out by Martin Schwidefsky.

This cleanup make a barrier added by
5aee405c662ca644980c184774277fc6d0769a84 needless.  So this patch removes
it.

As a bonus, this cleanup make wall_jiffies can be removed easily, since now
wall_jiffies is always synced with jiffies.  (This patch does not really
remove wall_jiffies.  It would be another cleanup patch)

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Acked-by: Russell King <rmk@arm.linux.org.uk>
Cc: Ian Molton <spyro@f2s.com>
Cc: Mikael Starvik <starvik@axis.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Hirokazu Takata <takata.hirokazu@renesas.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Kazumoto Kojima <kkojima@rr.iij4u.or.jp>
Cc: Richard Curnow <rc@rc0.org.uk>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Miles Bader <uclinux-v850@lsi.nec.co.jp>
Cc: Chris Zankel <chris@zankel.net>
Acked-by: "Luck, Tony" <tony.luck@intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 13 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index a2cb1ecb1b28..4f55622b0d38 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1222,10 +1222,8 @@ static inline void calc_load(unsigned long ticks)
         unsigned long active_tasks; /* fixed-point */
         static int count = LOAD_FREQ;
 
-        count -= ticks;
-        if (count < 0) {
-                count += LOAD_FREQ;
-                active_tasks = count_active_tasks();
+        active_tasks = count_active_tasks();
+        for (count -= ticks; count < 0; count += LOAD_FREQ) {
                 CALC_LOAD(avenrun[0], EXP_1, active_tasks);
                 CALC_LOAD(avenrun[1], EXP_5, active_tasks);
                 CALC_LOAD(avenrun[2], EXP_15, active_tasks);
@@ -1270,11 +1268,8 @@ void run_local_timers(void)
  * Called by the timer interrupt. xtime_lock must already be taken
  * by the timer IRQ!
  */
-static inline void update_times(void)
+static inline void update_times(unsigned long ticks)
 {
-        unsigned long ticks;
-
-        ticks = jiffies - wall_jiffies;
         wall_jiffies += ticks;
         update_wall_time();
         calc_load(ticks);
@@ -1286,12 +1281,10 @@ static inline void update_times(void)
  * jiffies is defined in the linker script...
  */
 
-void do_timer(struct pt_regs *regs)
+void do_timer(unsigned long ticks)
 {
-        jiffies_64++;
-        /* prevent loading jiffies before storing new jiffies_64 value. */
-        barrier();
-        update_times();
+        jiffies_64 += ticks;
+        update_times(ticks);
 }
 
 #ifdef __ARCH_WANT_SYS_ALARM