[valgrind] [Bug 394307] New: Add macro to extract current instruction count for peak load monitoring

[Jonas Josefsson]

https://bugs.kde.org/show_bug.cgi?id=394307

            Bug ID: 394307
           Summary: Add macro to extract current instruction count for
                    peak load monitoring
           Product: valgrind
           Version: unspecified
          Platform: Other
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: callgrind
          Assignee: josef.weidendor...@gmx.de
          Reporter: jonjo...@gmail.com
  Target Milestone: ---

In order to use callgrind to find load peaks, it is necessary to extract the
current instruction count from the running program. Currently callgrind just
gives the total instruction count which can give information about a mean load
but it cannot be used to find peak loads.

I've made a modification to callgrind that adds a macro that does this:

diff --git a/callgrind/callgrind.h b/callgrind/callgrind.h
index f078cc82b..6d3c40951 100644
--- a/callgrind/callgrind.h
+++ b/callgrind/callgrind.h
@@ -78,7 +78,8 @@ typedef
       VG_USERREQ__TOGGLE_COLLECT,
       VG_USERREQ__DUMP_STATS_AT,
       VG_USERREQ__START_INSTRUMENTATION,
-      VG_USERREQ__STOP_INSTRUMENTATION
+      VG_USERREQ__STOP_INSTRUMENTATION,
+      VG_USERREQ__GET_TOTAL_COSTS
    } Vg_CallgrindClientRequest;

 /* Dump current state of cost centers, and zero them afterwards */
@@ -126,4 +127,10 @@ typedef
   VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__STOP_INSTRUMENTATION,  \
                                   0, 0, 0, 0, 0)

+#define CALLGRIND_GET_TOTAL_COSTS(rValue)                        \
+  VALGRIND_DO_CLIENT_REQUEST(rValue, 0, VG_USERREQ__GET_TOTAL_COSTS,  \
+                                  0, 0, 0, 0, 0)
+
 #endif /* __CALLGRIND_H */
diff --git a/callgrind/main.c b/callgrind/main.c
index ab4927296..dd59cc208 100644
--- a/callgrind/main.c
+++ b/callgrind/main.c
@@ -1661,6 +1661,20 @@ Bool CLG_(handle_client_request)(ThreadId tid, UWord
*args, UWord *ret)
      }
      break;

+  case VG_USERREQ__GET_TOTAL_COSTS:
+     {
+        #define UWORD_MAX (~(UWord)0)
+        ULong Ir_total;
+
+        Ir_total = CLG_(current_state).cost[ fullOffset(EG_IR) ];
+        
+        if (Ir_total > UWORD_MAX) // ULong is 64 bits, UWord might be 32 bit
+          Ir_total = UWORD_MAX;
+
+        *ret = ((UWord) Ir_total);
+     }
+     break;
+
    case VG_USERREQ__ZERO_STATS:
      CLG_(zero_all_cost)(True);
       *ret = 0;                 /* meaningless */
(END)


This can be used to track the peak load of a function in the following way:

// Some kind of main loop
unsigned long MaxInstCount = 0;
while(1) 
{
    unsigned long PostInstCount, PreInstCount;

    CALLGRIND_ZERO_STATS;
    CALLGRIND_START_INSTRUMENTATION;

    CALLGRIND_GET_TOTAL_COSTS(PreInstCount);

    // Execute function to monitor
    Execute_Something();

    CALLGRIND_GET_TOTAL_COSTS(PostInstCount);

    PostInstCount -= PreInstCount;

    // Find max and dump callgrind stats.
    if (PostInstCount > MaxInstCount)
    {    
         MaxInstCount = PostInstCount;
         CALLGRIND_DUMP_STATS;
    }

    // Write execution time and some other parameters to
InstructionFetchLog.txt.
    fprintf(InstructionFetchLog, "%u,%u\n", PostInstCount,
SomeInterestingStateInfo);

    // Stop intrumentation
    CALLGRIND_STOP_INSTRUMENTATION;
}

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