sched/{fair,tune}: use reciprocal_value to compute boost margin

Change-Id: I493b07360c46eee0b72c2a046dab9ec6cb3427ef
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Srinath Sridharan <srinathsr@google.com>

kernel/sched/fair.c

@@ -5805,6 +5805,8 @@ static bool cpu_overutilized(int cpu)
 
 #ifdef CONFIG_SCHED_TUNE
 
+struct reciprocal_value schedtune_spc_rdiv;
+
 static long
 schedtune_margin(unsigned long signal, long boost)
 {
@@ -5815,29 +5817,16 @@ schedtune_margin(unsigned long signal, long boost)
 	 *
 	 * The Boost (B) value is used to compute a Margin (M) which is
 	 * proportional to the complement of the original Signal (S):
-	 *   M = B * (SCHED_LOAD_SCALE - S), if B is positive
+	 *   M = B * (SCHED_CAPACITY_SCALE - S)
-	 *   M = B * S, if B is negative
 	 * The obtained M could be used by the caller to "boost" S.
 	 */
 	if (boost >= 0) {
-		margin  = SCHED_LOAD_SCALE - signal;
+		margin  = SCHED_CAPACITY_SCALE - signal;
 		margin *= boost;
 	} else
 		margin = -signal * boost;
-	/*
+
-	 * Fast integer division by constant:
+	margin  = reciprocal_divide(margin, schedtune_spc_rdiv);
-	 *  Constant   :                 (C) = 100
-	 *  Precision  : 0.1%            (P) = 0.1
-	 *  Reference  : C * 100 / P     (R) = 100000
-	 *
-	 * Thus:
-	 *  Shift bits : ceil(log(R,2))  (S) = 17
-	 *  Mult const : round(2^S/C)    (M) = 1311
-	 *
-	 *
-	 */
-	margin  *= 1311;
-	margin >>= 17;
 
 	if (boost < 0)
 		margin *= -1;

kernel/sched/tune.c

@@ -17,6 +17,7 @@ static bool schedtune_initialized = false;
 
 unsigned int sysctl_sched_cfs_boost __read_mostly;
 
+extern struct reciprocal_value schedtune_spc_rdiv;
 extern struct target_nrg schedtune_target_nrg;
 
 /* Performance Boost region (B) threshold params */
@@ -937,6 +938,8 @@ schedtune_init(void)
 	pr_info("schedtune: configured to support global boosting only\n");
 #endif
 
+	schedtune_spc_rdiv = reciprocal_value(100);
+
 	return 0;
 
 nodata: