For simplicity of the explanation let's consider the following notations:
m = max_block_cpu_usage
t = block-time
e = last-block-cpu-effort-percent
w = block_time_interval = 500ms
a = produce-block-early-amount = (w - w*e/100) ms
p = produce-block-time; p = t - a
c = billed_cpu_in_block = minimum(m, w - a)
n = network tcp/ip latency
peer validation for similar hardware/eosio-version/config will be <= m
Let's consider for exemplification the following four BPs and their network topology as depicted in below diagram
BP-A will send block at p and,
BP-B needs block at time t or otherwise will drop it.
If BP-Ais producing 12 blocks as follows b(lock) at t(ime) 1, bt 1.5, bt 2, bt 2.5, bt 3, bt 3.5, bt 4, bt 4.5, bt 5, bt 5.5, bt 6, bt 6.5 then BP-B needs bt 6.5 by time 6.5 so it has .5 to produce bt 7.
Please notice that the time of bt 7 minus .5 equals the time of bt 6.5 therefore time t is the last block time of BP-A and when BP-B needs to start its first block.
Example 1
BP-A has 50% e, m = 200ms, c = 200ms, n = 0ms, a = 250ms:
BP-A sends at (t-250ms) <-> BP-A-Peer processes for 200ms and sends at (t - 50ms) <-> BP-B-Peer processes for 200ms and sends at (t + 150ms) <-> arrive at BP-B 150ms too late.
Example 2
BP-A has 40% e and m = 200ms, c = 200ms, n = 0ms, a = 300ms:
(t-300ms) <-> (+200ms) <-> (+200ms) <-> arrive at BP-B 100ms too late.
Example 3
BP-A has 30% e and m = 200ms, c = 150ms, n = 0ms, a = 350ms:
(t-350ms) <-> (+150ms) <-> (+150ms) <-> arrive at BP-B with 50ms to spare.
Example 4
BP-A has 25% e and m = 200ms, c = 125ms, n = 0ms, a = 375ms:
(t-375ms) <-> (+125ms) <-> (+125ms) <-> arrive at BP-B with 125ms to spare.
Example 5
BP-A has 10% e and m = 200ms, c = 50ms, n = 0ms, a = 450ms:
(t-450ms) <-> (+50ms) <-> (+50ms) <-> arrive at BP-B with 350ms to spare.
Example 6
BP-A has 10% e and m = 200ms, c = 50ms, n = 15ms, a = 450ms:
(t-450ms) <- +15ms -> (+50ms) <- +15ms -> (+50ms) <- +15ms -> BP-B <-> arrive with 305ms to spare.
Example 7
Example world-wide network:BP-Ahas 10% e and m = 200ms, c = 50ms, n = 15ms/250ms, a = 450ms:
(t-450ms) <- +15ms -> (+50ms) <- +250ms -> (+50ms) <- +15ms -> BP-B <-> arrive with 70ms to spare.
Running wasm-runtime=eos-vm-jit eos-vm-oc-enable on relay node will reduce the validation time.