Plan: staticdeps eval

plan/60_staticdeps.md

@@ -113,7 +113,47 @@ On SKX,
 
 ### Dependencies detection
 
-TODO
+#### With valgrind
+
+* Instrument binary:
+    * for each write, add `write_addr -> writer_pc` to a hashmap
+    * for each read, fetch `writer_pc` from hashmap
+        * if found, add a dependency `reader_pc -> writer_pc`
+    * At the end, write deps file:
+        * `#occur, src_elf_pc, src_elf_path, dst_elf_pc, dst_elf_path`
+    * Run for each binary in genbenchs
+
+* For each binary in genbenchs,
+    * for each BB with more than 10% of max BB hits,
+    * predict deps with staticdeps
+    * check which dependencies are found/missed from the instrumented ones
+    * limitation: will only find deps from/to the same BB! Dependencies leaving
+      a BB are discarded.
+
+* Result: about 38% of deps found.
+
+* Cause: kernels executed in loops.
+    * No dependency in the kernel
+    ```
+    while:
+        read (%rax)
+        %rax ++
+        write (%rax)
+    ```
+    * But dependencies if executed in a loop! "Unwanted" deps.
+    * and irrelevant in real life anyway: they are far away and will not cause
+      latency
+* Fix: introduce dependency lifetime
+    * timestamp = instructions executed (VG instrumentation, added up at the
+      end of each BB)
+    * lifetime fixed to 1024 instructions
+    * dependencies are discarded if written to more than a lifetime ago
+
+* Result: about (?? TODO) of deps found
+
+#### With Gus
+
+TODO ?
 
 ### UiCA enriching