change invoke time to "TImer" and add time/insn ratio histogram

Author: jayz22

docs/metrics.md

@@ -176,9 +176,11 @@ soroban.host-fn-op.emit-event                | meter     | number of events emit
 soroban.host-fn-op.emit-event-byte           | meter     | number of event bytes emitted
 soroban.host-fn-op.cpu-insn                  | meter     | metered cpu instructions
 soroban.host-fn-op.mem-byte                  | meter     | metered memory bytes
-soroban.host-fn-op.invoke-time-nsecs         | meter     | time [nsecs] spent in `invoke_host_function`
+soroban.host-fn-op.invoke-time-nsecs         | timer     | time spent in `invoke_host_function`
 soroban.host-fn-op.cpu-insn-excl-vm          | meter     | metered cpu instructions excluding VM instantation
-soroban.host-fn-op.invoke-time-nsecs-excl-vm | meter     | time [nsecs] spent in `invoke_host_function` excluding VM instantation
+soroban.host-fn-op.invoke-time-nsecs-excl-vm | timer     | time spent in `invoke_host_function` excluding VM instantation
+soroban.host-fn-op.invoke-time-fsecs-cpu-insn-ratio         | histogram | ratio between invoke_time (femto-seconds) and cpu instructions
+soroban.host-fn-op.invoke-time-fsecs-cpu-insn-ratio-excl-vm | histogram | ratio between invoke_time (femto-seconds) and cpu instructions excluding VM instantation
 soroban.host-fn-op.max-rw-key-byte           | meter     | bytes of the largest key in entries read/written
 soroban.host-fn-op.max-rw-data-byte          | meter     | bytes of the largest data entry read/written
 soroban.host-fn-op.max-rw-code-byte          | meter     | bytes of the largest code entry read/written

src/transactions/InvokeHostFunctionOpFrame.cpp

@@ -225,15 +225,24 @@ struct HostFunctionMetrics
             .NewMeter({"soroban", "host-fn-op", "mem-byte"}, "byte")
             .Mark(mMemByte);
         mMetrics.registry()
-            .NewMeter({"soroban", "host-fn-op", "invoke-time-nsecs"}, "time")
-            .Mark(mInvokeTimeNsecs);
+            .NewTimer({"soroban", "host-fn-op", "invoke-time-nsecs"})
+            .Update(std::chrono::nanoseconds(mInvokeTimeNsecs));
         mMetrics.registry()
             .NewMeter({"soroban", "host-fn-op", "cpu-insn-excl-vm"}, "insn")
             .Mark(mCpuInsnExclVm);
         mMetrics.registry()
-            .NewMeter({"soroban", "host-fn-op", "invoke-time-nsecs-excl-vm"},
-                      "time")
-            .Mark(mInvokeTimeNsecsExclVm);
+            .NewTimer({"soroban", "host-fn-op", "invoke-time-nsecs-excl-vm"})
+            .Update(std::chrono::nanoseconds(mInvokeTimeNsecsExclVm));
+        mMetrics.registry()
+            .NewHistogram(
+                {"soroban", "host-fn-op", "invoke-time-fsecs-cpu-insn-ratio"})
+            .Update(mInvokeTimeNsecs * 1000000 /
+                    std::max(mCpuInsn, uint64_t(1)));
+        mMetrics.registry()
+            .NewHistogram({"soroban", "host-fn-op",
+                           "invoke-time-fsecs-cpu-insn-ratio-excl-vm"})
+            .Update(mInvokeTimeNsecsExclVm * 1000000 /
+                    std::max(mCpuInsnExclVm, uint64_t(1)));
 
         mMetrics.registry()
             .NewMeter({"soroban", "host-fn-op", "max-rw-key-byte"}, "byte")