scx_p2dq: Add energy-aware scheduling with thermal and frequency awareness

Implement energy-aware scheduling (EAS) for big.LITTLE architectures.

Key features:
- Thermal pressure tracking infrastructure using cpu_ctx->perf field
- Frequency-invariant effective capacity calculation using scx_bpf_cpuperf_cur()
- Energy-aware idle CPU selection with thermal, capacity, and cost scoring
- Thermal-aware CPU selection for MODE_PERF and MODE_EFFICIENCY paths
- Task placement based on utilization (little cores for <25%, big cores for >75%)

Implementation details:
- get_effective_cpu_capacity() now scales by frequency: (base - thermal) * freq / 1024
- select_best_idle_cpu() scores CPUs: capacity * 10 - energy_cost / 10
- pick_idle_energy_aware() handles preferred/fallback core type selection
- pick_idle_thermal_aware() provides lightweight thermal avoidance for mode-based scheduling

Statistics added for monitoring:
- P2DQ_STAT_THERMAL_KICK/AVOID: Thermal pressure events
- P2DQ_STAT_EAS_LITTLE_SELECT/BIG_SELECT/FALLBACK: EAS placement decisions

Enable with --enable-eas true flag.

Signed-off-by: Daniel Hodges <[email protected]>

Author: hodgesds

scheds/rust/scx_p2dq/src/bpf/intf.h

@@ -84,6 +84,11 @@ enum stat_idx {
 	P2DQ_STAT_WAKE_PREV,
 	P2DQ_STAT_WAKE_LLC,
 	P2DQ_STAT_WAKE_MIG,
+	P2DQ_STAT_THERMAL_KICK,		/* CPU kicks due to thermal pressure */
+	P2DQ_STAT_THERMAL_AVOID,	/* Times throttled CPUs avoided */
+	P2DQ_STAT_EAS_LITTLE_SELECT,	/* Task placed on little core via EAS */
+	P2DQ_STAT_EAS_BIG_SELECT,	/* Task placed on big core via EAS */
+	P2DQ_STAT_EAS_FALLBACK,		/* EAS fallback to non-preferred core */
 	P2DQ_NR_STATS,
 };