+/*
+ * On some AMD platforms, MWAITX has a configurable 32-bit timer, that
+ * counts with TSC frequency. The input value is the loop of the
+ * counter, it will exit when the timer expires.
+ */
+static void delay_mwaitx(unsigned long __loops)
+{
+ u64 start, end, delay, loops = __loops;
+
+ start = rdtsc_ordered();
+
+ for (;;) {
+ delay = min_t(u64, MWAITX_MAX_LOOPS, loops);
+
+ /*
+ * Use cpu_tss as a cacheline-aligned, seldomly
+ * accessed per-cpu variable as the monitor target.
+ */
+ __monitorx(this_cpu_ptr(&cpu_tss), 0, 0);
+
+ /*
+ * AMD, like Intel, supports the EAX hint and EAX=0xf
+ * means, do not enter any deep C-state and we use it
+ * here in delay() to minimize wakeup latency.
+ */
+ __mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE);
+
+ end = rdtsc_ordered();
+
+ if (loops <= end - start)
+ break;
+
+ loops -= end - start;
+
+ start = end;
+ }
+}
+