Closed-Loop Throughput (Little's Law)
X_turn =
C / (
R +
Z)
X_task =
X_turn /
N
Per-Turn Latency
R(j) = TTFT(
L_prefill) + TPOT(
B_eff) ×
OSL
L_prefill = h·ΔL + (1−h)·L(j)
TPOT (Decode Step Time)
TPOT = max(
T_weight +
T_kv,
T_compute)
T_weight = ModelBytes / BW
T_kv = B × L_avg × KV_bytes / BW
Active Ratio & GPU Utilization
ρ =
R / (
R +
Z)
B_eff = C × ρ
GPU util = min(B_eff, B_max) / B_max
KV-Cache Memory Constraint
C_max = M_avail / (L_avg × KV_bytes_per_token)
L_avg = L₀ + (N/2) × (OSL + ΔL)
Prefix Cache Benefit
TTFT_cache = f(ΔL) ≪ TTFT_full = f(L_avg)
Speedup = R_nocache / R_cache