RFR: 8252093: formula used to calculate decaying variance in numberSeq

[Albert Yang]

 > Did you compare the total runtime of the two ZGC runs,
Yes.

 > the extra cycles could be caused warmup taking much longer in the second run.
Seem so. Before the patch, it takes 40 GC cycles to warmup, but after the patch, 78 GC 
cycles. If we take that into account, the actual GC cycles during the measurement 
(349-40=309 vs 380-78=302) are very close.

```
# before
[2.610s][info][gc] GC(0) Garbage Collection (System.gc()) 2480M(2%)->176M(0%)
[86.779s][info][gc] GC(1) Garbage Collection (System.gc()) 4796M(4%)->1464M(1%)
[323.875s][info][gc] GC(12) Garbage Collection (System.gc()) 50576M(39%)->1646M(1%)
[421.629s][info][gc] GC(17) Garbage Collection (System.gc()) 41726M(32%)->1628M(1%)
[608.851s][info][gc] GC(33) Garbage Collection (System.gc()) 22748M(17%)->1826M(1%)
[686.220s][info][gc] GC(39) Garbage Collection (System.gc()) 34834M(27%)->1834M(1%)
[692.493s][info][gc] GC(40) Garbage Collection (System.gc()) 8180M(6%)->1346M(1%)
[7867.090s][info][gc] GC(349) Garbage Collection (System.gc()) 21014M(16%)->424M(0%)
[8045.531s][info][gc] GC(356) Garbage Collection (System.gc()) 60270M(46%)->1796M(1%)
[8051.900s][info][gc] GC(357) Garbage Collection (System.gc()) 8286M(6%)->1350M(1%)
```

```
# after
[2.632s][info][gc] GC(0) Garbage Collection (System.gc()) 2480M(2%)->176M(0%)
[86.816s][info][gc] GC(1) Garbage Collection (System.gc()) 4774M(4%)->1468M(1%)
[313.601s][info][gc] GC(12) Garbage Collection (System.gc()) 55236M(42%)->280M(0%)
[408.054s][info][gc] GC(18) Garbage Collection (System.gc()) 65486M(50%)->1784M(1%)
[590.894s][info][gc] GC(35) Garbage Collection (System.gc()) 20584M(16%)->422M(0%)
[690.631s][info][gc] GC(45) Garbage Collection (System.gc()) 22204M(17%)->1638M(1%)
[791.317s][info][gc] GC(57) Garbage Collection (System.gc()) 21268M(16%)->436M(0%)
[908.128s][info][gc] GC(68) Garbage Collection (System.gc()) 40480M(31%)->1838M(1%)
[989.525s][info][gc] GC(77) Garbage Collection (System.gc()) 6198M(5%)->440M(0%)
[995.913s][info][gc] GC(78) Garbage Collection (System.gc()) 7064M(5%)->1362M(1%)
[8024.034s][info][gc] GC(380) Garbage Collection (System.gc()) 20714M(16%)->438M(0%)
[8196.327s][info][gc] GC(388) Garbage Collection (System.gc()) 12494M(10%)->436M(0%)
[8202.587s][info][gc] GC(389) Garbage Collection (System.gc()) 6920M(5%)->1354M(1%)
```

-- 
/Albert