Google adds cycle-level kernel profiling to XProf for TPU v7

KEY POINTS

1. Google added a Kernel Profiling suite to XProf (the OpenXLA/JAX profiler), exposing cycle-level details for custom kernels (e.g., Pallas) and sampling hardware performance counters on TPU v7 (Ironwood).
2. The tooling shows lowered MLIR, per-unit time-aligned counter tracks, a Perf Counters view with ~16,000 raw counters, and supports periodic sampling (1µs floor) or external-triggered sub-microsecond capture; a Google demo using triple buffering reduced a matmul kernel from 125.5µs to 88µs.
3. This gives kernel authors and TPU users register-level ground-truth telemetry for custom-compiled kernels, addressing inaccuracies in XLA static cost models and enabling more precise performance tuning.