sched/fair: Fix comments

Historically our periods (or p) argument in PELT denoted the number of
full periods (what is now d2). However recent patches have changed
this to the total decay (previously p+1), leading to a confusing
discrepancy between comments and code.

Try and clarify things by making periods (in code) and p (in comments)
be the same thing (again).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -2777,18 +2777,18 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
 	u32 c1, c2, c3 = d3; /* y^0 == 1 */
 
 	/*
-	 * c1 = d1 y^(p+1)
+	 * c1 = d1 y^p
 	 */
 	c1 = decay_load((u64)d1, periods);
 
 	/*
-	 *             p
+	 *            p-1
 	 * c2 = 1024 \Sum y^n
 	 *            n=1
 	 *
 	 *              inf        inf
 	 *    = 1024 ( \Sum y^n - \Sum y^n - y^0 )
-	 *              n=0        n=p+1
+	 *              n=0        n=p
 	 */
 	c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024;
 
@@ -2808,14 +2808,14 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
  *         |<->|<----------------->|<--->|
  * ... |---x---|------| ... |------|-----x (now)
  *
- *                                p
- * u' = (u + d1) y^(p+1) + 1024 \Sum y^n + d3 y^0
+ *                           p-1
+ * u' = (u + d1) y^p + 1024 \Sum y^n + d3 y^0
  *                           n=1
  *
- *    = u y^(p+1) +				(Step 1)
+ *    = u y^p +					(Step 1)
  *
- *                          p
- *      d1 y^(p+1) + 1024 \Sum y^n + d3 y^0	(Step 2)
+ *                     p-1
+ *      d1 y^p + 1024 \Sum y^n + d3 y^0		(Step 2)
  *                     n=1
  */
 static __always_inline u32