kernel: time: Add delay after cpu_relax() in tight loops

Tight loops of spin_lock_irqsave() and spin_unlock_irqrestore()
in timer and hrtimer are causing scheduling delays. Add delay of
few nano seconds after cpu_relax in the timer/hrtimer tight loops.

Change-Id: Iaa0ab92da93f7b245b1d922b6edca2bebdc0fbce
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>

kernel/time/hrtimer.c

@@ -51,6 +51,7 @@
 #include <linux/timer.h>
 #include <linux/freezer.h>
 #include <linux/compat.h>
+#include <linux/delay.h>
 
 #include <linux/uaccess.h>
 
@@ -178,6 +179,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
 			raw_spin_unlock_irqrestore(&base->cpu_base->lock, *flags);
 		}
 		cpu_relax();
+		ndelay(TIMER_LOCK_TIGHT_LOOP_DELAY_NS);
 	}
 }
 
@@ -1182,6 +1184,7 @@ int hrtimer_cancel(struct hrtimer *timer)
 		if (ret >= 0)
 			return ret;
 		cpu_relax();
+		ndelay(TIMER_LOCK_TIGHT_LOOP_DELAY_NS);
 	}
 }
 EXPORT_SYMBOL_GPL(hrtimer_cancel);

kernel/time/tick-internal.h

@@ -163,3 +163,4 @@ DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);
 
 extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem);
 void timer_clear_idle(void);
+#define TIMER_LOCK_TIGHT_LOOP_DELAY_NS	350

kernel/time/timer.c

@@ -957,6 +957,7 @@ static struct timer_base *lock_timer_base(struct timer_list *timer,
 			raw_spin_unlock_irqrestore(&base->lock, *flags);
 		}
 		cpu_relax();
+		ndelay(TIMER_LOCK_TIGHT_LOOP_DELAY_NS);
 	}
 }
 
@@ -1310,6 +1311,7 @@ int del_timer_sync(struct timer_list *timer)
 		if (ret >= 0)
 			return ret;
 		cpu_relax();
+		ndelay(TIMER_LOCK_TIGHT_LOOP_DELAY_NS);
 	}
 }
 EXPORT_SYMBOL(del_timer_sync);