[Issue 20118] New: rt/trace: rdtsc is unordered without preceding memory barrie

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20118

          Issue ID: 20118
           Summary: rt/trace: rdtsc is unordered without preceding memory
                    barrie
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: kubo39 at gmail.com

RDTSC is not ordered on Intel and AMD CPUs without preceding memory
barrier, and worse, the results can be non-monotonic if compared on
different processors.

The intel SDM says lfence;rdtsc causes all previous instrusctions to
complete before the tsc read, and AMD APM says to use mfence;rdtsc to
do same thing. This is what GNU/Linux kernel does on its rdtsc_ordered
function.

*
https://github.com/torvalds/linux/blob/03b9730b769fc4d87e40f6104f4c5b2e43889f19/arch/x86/include/asm/msr.h#L130-L154

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