docs: add inline comments about flush_cache and rotating buffer

include/ck_tile/host/flush_icache.hpp

@@ -6,6 +6,12 @@
 #include <hip/hip_runtime.h>
 
 namespace ck_tile {
+// GPU kernel to invalidate instruction cache for accurate benchmarking.
+// s_icache_inv: Asynchronously invalidates the L1 instruction cache on this compute unit,
+//               forcing subsequent kernel runs to fetch instructions from HBM instead of cache.
+// 16x s_nop:    Wait cycles (~16 cycles) to ensure cache invalidation completes before kernel
+//               exits. Without these NOPs, the flush may not finish, leading to inconsistent
+//               timing measurements where some instructions remain cached.
 static __global__ void flush_cache()
 {
     asm __volatile__("s_icache_inv \n\t"