kernel: add function to calculate delta between two cycle timestamps

include/socks/cpu.h

@@ -36,6 +36,10 @@ extern void cpu_set_available(unsigned int cpu_id);
 extern void cpu_set_online(unsigned int cpu_id);
 
 extern cycles_t get_cycles(void);
+static inline cycles_t cycles_diff(cycles_t then, cycles_t now)
+{
+	return now >= then ? now - then : (CYCLES_MAX - then) + now;
+}
 
 #define irq_enable() ml_int_enable()
 #define irq_disable() ml_int_disable()

include/socks/types.h

@@ -3,6 +3,8 @@
 
 #include <stdint.h>
 
+#define CYCLES_MAX UINT64_MAX
+
 typedef uintptr_t phys_addr_t;
 typedef uint64_t cycles_t;