static inline uint64_t
_ns_to_clks(uint64_t ns)
{
- unsigned __int128 clkns = rte_get_tsc_hz();
+ /*
+ * clkns needs to be divided by 1E9 to get ns clocks. However,
+ * dividing by this first would lose a lot of accuracy.
+ * Dividing after a multiply by ns, could cause overflow of
+ * uint64_t if ns is about 5 seconds [if we assume a max tsc
+ * rate of 4GHz]. Therefore we first divide by 1E4, then
+ * multiply and finally divide by 1E5. This allows ns to be
+ * values many hours long, without overflow, while still keeping
+ * reasonable accuracy.
+ */
+ uint64_t clkns = rte_get_tsc_hz() / 1e4;
clkns *= ns;
- clkns /= 1000000000;
- return (uint64_t) clkns;
+ clkns /= 1e5;
+
+ return clkns;
}