sparc64: optimize loads in clock_sched()

In clock sched we now have three loads:
	- Function pointer
	- quotient for multiplication
	- offset

However, it is possible to improve performance substantially, by
guaranteeing that all three loads are from the same cacheline.

By moving these three values first in sparc64_tick_ops, and by having
tick_operations 64-byte aligned we guarantee this.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 12 insertions, 10 deletions

diff --git a/arch/sparc/include/asm/timer_64.h b/arch/sparc/include/asm/timer_64.h
index fce415034000..bde2cc40ae02 100644
--- a/arch/sparc/include/asm/timer_64.h
+++ b/arch/sparc/include/asm/timer_64.h
@@ -9,7 +9,12 @@
 #include <linux/types.h>
 #include <linux/init.h>
 
+/* The most frequently accessed fields should be first,
+ * to fit into the same cacheline.
+ */
 struct sparc64_tick_ops {
+        unsigned long ticks_per_nsec_quotient;
+        unsigned long offset;
         unsigned long long (*get_tick)(void);
         int (*add_compare)(unsigned long);
         unsigned long softint_mask;
diff --git a/arch/sparc/kernel/time_64.c b/arch/sparc/kernel/time_64.c
index 5f53b74dd493..44e37e9f8428 100644
--- a/arch/sparc/kernel/time_64.c
+++ b/arch/sparc/kernel/time_64.c
@@ -164,7 +164,7 @@ static unsigned long tick_add_tick(unsigned long adj)
         return new_tick;
 }
 
-static struct sparc64_tick_ops tick_operations __read_mostly = {
+static struct sparc64_tick_ops tick_operations __cacheline_aligned = {
         .name           =       "tick",
         .init_tick      =       tick_init_tick,
         .disable_irq    =       tick_disable_irq,
@@ -391,9 +391,6 @@ static struct sparc64_tick_ops hbtick_operations __read_mostly = {
         .softint_mask   =       1UL << 0,
 };
 
-static unsigned long timer_ticks_per_nsec_quotient __read_mostly;
-static unsigned long timer_offset __read_mostly;
-
 unsigned long cmos_regs;
 EXPORT_SYMBOL(cmos_regs);
 
@@ -784,11 +781,11 @@ void __init time_init(void)
 
         tb_ticks_per_usec = freq / USEC_PER_SEC;
 
-        timer_ticks_per_nsec_quotient =
+        tick_operations.ticks_per_nsec_quotient =
                 clocksource_hz2mult(freq, SPARC64_NSEC_PER_CYC_SHIFT);
 
-        timer_offset = (tick_operations.get_tick()
-                        * timer_ticks_per_nsec_quotient)
+        tick_operations.offset = (tick_operations.get_tick()
+                        * tick_operations.ticks_per_nsec_quotient)
                         >> SPARC64_NSEC_PER_CYC_SHIFT;
 
         clocksource_tick.name = tick_operations.name;
@@ -816,11 +813,11 @@ void __init time_init(void)
 
 unsigned long long sched_clock(void)
 {
+        unsigned long quotient = tick_operations.ticks_per_nsec_quotient;
+        unsigned long offset = tick_operations.offset;
         unsigned long ticks = tick_operations.get_tick();
 
-        return ((ticks * timer_ticks_per_nsec_quotient)
-                >> SPARC64_NSEC_PER_CYC_SHIFT)
-                - timer_offset;
+        return ((ticks * quotient) >> SPARC64_NSEC_PER_CYC_SHIFT) - offset;
 }
 
 int read_current_timer(unsigned long *timer_val)