+/*
+ * Return a CPU-local timestamp in nano-seconds. This timestamp is
+ * NOT synchronized across CPUs its return value must never be
+ * compared against the values returned on another CPU. The usage in
+ * kernel/sched.c ensures that.
+ *
+ * The return-value of sched_clock() is NOT supposed to wrap-around.
+ * If it did, it would cause some scheduling hiccups (at the worst).
+ * Fortunately, with a 64-bit cycle-counter ticking at 100GHz, even
+ * that would happen only once every 5+ years.
+ *
+ * The code below basically calculates:
+ *
+ * (ia64_get_itc() * local_cpu_data->nsec_per_cyc) >> IA64_NSEC_PER_CYC_SHIFT
+ *
+ * except that the multiplication and the shift are done with 128-bit
+ * intermediate precision so that we can produce a full 64-bit result.
+ */
+GLOBAL_ENTRY(sched_clock)
+ addl r8=THIS_CPU(cpu_info) + IA64_CPUINFO_NSEC_PER_CYC_OFFSET,r0
+ mov.m r9=ar.itc // fetch cycle-counter (35 cyc)
+ ;;
+ ldf8 f8=[r8]
+ ;;
+ setf.sig f9=r9 // certain to stall, so issue it _after_ ldf8...
+ ;;
+ xmpy.lu f10=f9,f8 // calculate low 64 bits of 128-bit product (4 cyc)
+ xmpy.hu f11=f9,f8 // calculate high 64 bits of 128-bit product
+ ;;
+ getf.sig r8=f10 // (5 cyc)
+ getf.sig r9=f11
+ ;;
+ shrp r8=r9,r8,IA64_NSEC_PER_CYC_SHIFT
+ br.ret.sptk.many rp
+END(sched_clock)
+