Ceph

z Systems (aka s390x/s390) supports a time-of-day clock of 64-bits whose bit 63 every 2**-12 seconds, (Bit 53 equates to a microsecond.) This would appear to serve as the source for the rdtsc() method in Cycles.h. I have a PR ready that will provide this capability. This patch looks as follows:

--- a/src/common/Cycles.h
+++ b/src/common/Cycles.h
@@ -78,6 +78,12 @@ class Cycles {
     uint32_t lo = 0, hi = 0;
     asm volatile("mftbu %0; mftb %1" : "=r" (hi), "=r" (lo));
     return (((uint64_t)hi << 32) | lo);
+#elif defined(__s390__)
+    uint64_t tod;
+
+    asm volatile("     stck %0\n" 
+                : "=Q" (tod) : : "cc");
+    return (tod);
 #else
 #warning No high-precision counter available for your OS/arch
     return 0;

Note, this clock is a subset of a 128-bit clock kept by the hardware which supports multiple epochs. The base time for this clock is Jan 1 1900. The 64-bit subset will rollover in 2042.

The stck instruction guarantees a monotonically increasing value in a multiprocessor environment.