Performance improvement:

Makefile

@@ -270,6 +270,7 @@ check:
 	  mkdir -p $(COVER_DB) ;                                            \
 	  echo "*** Run once, force parallel ***" ;                         \
 	  LCOV_FORCE_PARALLEL=1 $(MAKE) -s -C tests check LCOV_HOME=`pwd` ; \
+	  LCOV_FORCE_PARALLEL=1 $(MAKE) -s -C example LCOV_HOME=`pwd` ;     \
 	  echo "*** Run again, no force ***" ;                              \
 	fi
 	@$(MAKE) -s -C tests check LCOV_HOME=`pwd`
@@ -293,7 +294,7 @@ else
 	@echo "Checking changes in source files for coding style issues (MODE=diff):"
 endif
 	@RC=0 ;                                                  \
-	CHECKFILES=`find . -path ./.git -prune -o \( \( -type f -exec grep -q '^#!.*perl' {} \; \) -o -name '*.pm' \) -not \( -name '*.tdy' -o -name '*.orig' -o -name '*~' \) -print `; \
+	CHECKFILES=`find bin lib scripts tests -path ./.git -prune -o \( \( -type f -exec grep -q '^#!.*perl' {} \; \) -o -name '*.pm' \) -not \( -name '*.tdy' -o -name '*.orig' -o -name '*~' \) -print `; \
 	for FILE in $$CHECKFILES ; do                            \
 	  $(CHECKSTYLE) "$$FILE";                                \
 	  if [ 0 != $$? ] ; then                                 \

README

@@ -1,6 +1,6 @@
 -------------------------------------------------
 - README file for the LTP GCOV extension (LCOV) -
-- Last changes: 2025-10-01
+- Last changes: 2026-02-10
 -------------------------------------------------
 
 Description
@@ -430,6 +430,9 @@ LCOV features and capabilities fall into 7 major categories:
         vii) compress the 'function detail' table to improve readability
              by shortening long C++ template and function names.
              Sample script:  simplify.pm
+        viii) use history from previous execution to improve runtime
+             performance of current execution by improving load balancing.
+             Sample script:  history.pm
 
      The callback may be any desired script or executable - but there
      may be performance advantages if it is written as a Perl module.
@@ -445,7 +448,7 @@ LCOV features and capabilities fall into 7 major categories:
      Related options:
        --annotate-script, --criteria-script, --version-script
        --resolve-script, --select-script, --context-script
-       --simplify-script
+       --simplify-script --history-script
 
   f) Performance
 
@@ -466,7 +469,7 @@ LCOV features and capabilities fall into 7 major categories:
 
      See the genhtml/lcov/geninfo man pages for details
 
-     Related options: --parallel, --memory, --profile
+     Related options: --parallel, --memory, --profile, --history-script
 
   g) Language/tool support
 

bin/geninfo

@@ -223,6 +223,7 @@ our $defaultChunkSize;
 our $defaultInterval;
 our %childRetryCounts;
 our @large_files;
+our $callFromLcov;
 
 our $cwd = getcwd();
 chomp($cwd);
@@ -243,6 +244,7 @@ $ENV{"LC_ALL"} = "C";
 
 # retrieve settings from RC file - use these if not overridden on command line
 my %geninfo_opts = ("test-name|t=s"       => \$test_name,
+                    'call-from-lcov'      => \$callFromLcov,
                     "output-filename|o=s" => \$output_filename,
                     "base-directory|b=s"  => \$base_directory,
                     "follow|f"            => \$lcovutil::opt_follow,
@@ -906,15 +908,15 @@ sub add_worklist_entry
 {
     my ($self, $filename, $directory) = @_;
     if (exists($self->[1]->{$filename})) {
-        lcovutil::ignorable_error(
-                                 $lcovutil::ERROR_USAGE,
-                                 "duplicate file $filename in both " .
-                                     $self->[1]->{$filename} . " and $directory"
-                                     .
-                                     (lcovutil::is_ignored(
+        lcovutil::ignorable_error($lcovutil::ERROR_USAGE,
+                                  "duplicate file $filename in both " .
+                                      $self->[1]->{$filename} .
+                                      " and $directory"
+                                      .
+                                      (lcovutil::is_ignored(
                                                        $lcovutil::ERROR_USAGE) ?
-                                          ' (skip latter)' :
-                                          ''));
+                                           ' (skip latter)' :
+                                           ''));
         return;
     }
     $self->[1]->{$filename} = $directory;
@@ -1333,8 +1335,45 @@ sub gen_info(@)
     }
     my @worklist;
     my $serialChunk = [1, []];
-    my $chunk       = [0, []];    # [isSerial, [fileList]]
-    FILE: foreach my $j (@$filelist) {
+    my $nChunks =
+        int(floor((scalar(@$filelist) + $chunkSize - 1) / $chunkSize));
+    for (my $i = 0; $i < $nChunks; ++$i) {
+        push(@worklist, [0, []]);
+    }
+    my $work = $filelist;    # default to the original order
+    if ($lcovutil::profileHistoryCallback &&
+        ($chunkSize > 1 || exists($ENV{LCOV_FORCE_PARALLEL}))) {
+        my (@predicted, @unknown);
+        foreach my $j (@$filelist) {
+            my ($dir, $gcda, $gcno) = @$j;
+            my $key       = defined($gcda) ? $gcda : $gcno;
+            my $k         = substr($key, length($dir) + 1);
+            my $predicted = $lcovutil::profileHistoryCallback->history($k);
+            if (defined($predicted)) {
+                push(@predicted, [$j, $predicted, $key]);
+            } else {
+                # put the ones we don't know about at the start of the list
+                #  - work on them first, trusting that we will have parallelism
+                #    capacity for the ones we know about
+                push(@unknown, $j);
+            }
+        }
+        @predicted =
+            sort({ $b->[1] <=> $a->[1] or $a->[2] cmp $b->[2] } @predicted);
+
+        lcovutil::info(scalar(@unknown) .
+                           ' (of ' . (scalar(@predicted) + scalar(@unknown)) .
+                           ") files do not appear in \'--history\' profile.\n")
+            if (@unknown);
+        if (@predicted) {
+            my @order = map({ $_->[0] } @predicted);
+            # unknown to the back...
+            push(@order, @unknown);
+            $work = \@order;
+        }
+    }
+    my $chunkId = 0;
+    FILE: foreach my $j (@$work) {
         my ($dir, $gcda, $gcno) = @$j;
         foreach my $f ($gcda, $gcno) {
             next unless defined($f);    # might not be a GCDA file
@@ -1345,15 +1384,15 @@ sub gen_info(@)
                 next FILE;
             }
         }
+        die("unexpected chunkId $chunkId") if $chunkId >= $nChunks;
+        my $chunk = $worklist[$chunkId++];
         push(@{$chunk->[1]}, $j);
-        if (scalar(@{$chunk->[1]}) == $chunkSize) {
-            push(@worklist, $chunk);
-            $chunk = [0, []];
+        if ($chunkId == $nChunks) {
+            $chunkId = 0;
         }
     }    #foreach DATA_FILE
-    push(@worklist, $chunk) if @{$chunk->[1]};
-    # serial chunk is at the top of the stack - so serial processing
-    #  happens before we fork multiple processes
+         # serial chunk is at the top of the stack - so serial processing
+         #  happens before we fork multiple processes
     push(@worklist, $serialChunk)
         if (@{$serialChunk->[1]});
 

bin/get_version.sh

@@ -25,7 +25,7 @@ else
 fi
 
 # Fallback
-[ -z "$VERSION" ] && VERSION="2.4"
+[ -z "$VERSION" ] && VERSION="2.4.1"
 [ -z "$RELEASE" ] && RELEASE="beta"
 [ -z "$FULL" ]    && FULL="$VERSION-$RELEASE"
 

bin/lcov

@@ -821,6 +821,7 @@ sub lcov_geninfo(@)
     @param = (File::Spec->catfile($tool_dir, 'geninfo'), @dir);
     # make things less confusing for user, by using the name they actually invoked
     push(@param, '--toolname', $lcovutil::tool_name);
+    push(@param, '--call-from-lcov');
     if ($output_filename) {
         push(@param, "--output-filename", $output_filename);
     }
@@ -914,6 +915,9 @@ sub lcov_geninfo(@)
     # memory has not been multiplied by Mb yet - so just pass the integer value
     push(@param, '--memory', $lcovutil::maxMemory)
         if defined($lcovutil::maxMemory);
+    # function coverage was enabled by default
+    push(@param, '--no-function-coverage')
+        if (!$lcovutil::func_coverage);
     push(@param, "--branch-coverage") if $lcovutil::br_coverage;
     push(@param, "--mcdc") if $lcovutil::mcdc_coverage;
     push(@param, '--fail-under-lines', $lcovutil::fail_under_lines)
@@ -935,6 +939,9 @@ sub lcov_geninfo(@)
                          ['--version-script', \@lcovutil::extractVersionScript],
                          ['--resolve-script', \@lcovutil::resolveCallback],
                          ['--substitute', \@lcovutil::file_subst_patterns],
+                         ['--history-script',
+                          \@lcovutil::profileHistoryCallback
+                         ],
                          ['--omit-lines', \@lcovutil::omit_line_patterns],
                          ['--erase-functions',
                           \@lcovutil::exclude_function_patterns

example/Makefile

@@ -83,7 +83,7 @@ gauss.o: methods/gauss.c gauss.h
 output: example descriptions test_noargs test_2_to_2000 test_overflow test_differential
 	@echo
 	@echo '*'
-	@echo '* Generating HTML output'
+	@echo '* Generating HTML output from data captured from tests'
 	@echo '*'
 	@echo
 	$(GENHTML) trace_noargs.info trace_args.info trace_overflow.info \
@@ -95,7 +95,7 @@ output: example descriptions test_noargs test_2_to_2000 test_overflow test_diffe
 	@echo '* See '`pwd`/output/index.html
 	@echo '*'
 	@echo
-	@echo "Generate HTML with hierarchical report and additional navigation features"
+	@echo "Generate HTML with hierarchical report and additional navigation features (same testcase data)"
 	@echo '*'
 	$(GENHTML) trace_noargs.info trace_args.info trace_overflow.info \
 		   --output-directory hierarchical \
@@ -175,7 +175,8 @@ test_differential:
 
 	@echo "Step 2: Capture initial coverage"
 	(cd $(REPO) ; \
-	$(LCOV) --capture -o baseline.info -d . --version-script $(SCRIPTDIR)/gitversion.pm )
+	$(LCOV) --capture -o baseline.info -d . \
+		--version-script $(SCRIPTDIR)/gitversion.pm --profile )
 
 	@echo "Step 3: Modify source code"
 	@(cd $(REPO) ; \
@@ -192,27 +193,34 @@ test_differential:
 	./example )
 
 	@echo "Step 5: Capture new coverage (after source changes)"
+	@echo "   (note that this example is too tiny for history reuse"
+	@echo "   to affect runtime performance)"
 	(cd $(REPO) ; \
-	 $(LCOV) --capture -o current.info -d . --version-script $(SCRIPTDIR)/gitversion.pm )
+	$(LCOV) --capture -o current.info -d .              \
+		--version-script $(SCRIPTDIR)/gitversion.pm \
+		--profile                                   \
+		--history $(SCRIPTDIR)/history.pm,baseline.info.json )
 	@echo "Compute source diffs"
 	(cd $(REPO) ;                                          \
 	$(SCRIPTDIR)/gitdiff -b . `git rev-list -n 1 baseline` \
 	  `git rev-list -n 1 current` > udiff.txt )
 
 	@echo "Step 6: Generate differential coverage report"
-	@echo "        (caching revision control data may result in improved runtime performance)"
+	@echo "      - caching revision control data may result in improved runtime performance)"
+	@echo "      - capture 'genhtml' execution profile that we can use later"
 	(cd $(REPO) ;                                            \
 	$(GENHTML) -o differential --baseline-file baseline.info \
 	  --diff-file udiff.txt --show-owners                    \
 	  --title "Differential coverage example"                \
 	  --annotate $(SCRIPTDIR)/gitblame.pm,--cache,./my_cache \
-	  --version-script $(SCRIPTDIR)/gitversion.pm            \
+	  --version-script $(SCRIPTDIR)/gitversion.pm --profile  \
 	  -- current.info )
 
 	@echo "point your browser to `realpath $(REPO)`/differential/index.html"
 
 	@echo "Step 7: Generate subset report for code review:"
-	@echo "        (reuse revision control data cached in previous step)"
+	@echo "      - reuse execution profile and cached revision control data"
+	@echo "        captured in previous step"
 	(cd $(REPO) ;                                            \
 	$(GENHTML) -o review --baseline-file baseline.info       \
 	  --diff-file udiff.txt --show-owners                    \
@@ -221,7 +229,9 @@ test_differential:
 	  --version-script $(SCRIPTDIR)/gitversion.pm            \
 	  --select-script $(SCRIPTDIR)/select.pm                 \
 	  --select-script --tla --select-script UNC,UIC,LBC      \
-	  -- current.info )
+	  --history-script $(SCRIPTDIR)/history.pm               \
+	  --history-script ./differential/genhtml.json --profile \
+          -- current.info )
 
 	@echo "point your browser to `realpath $(REPO)`/review/index.html"
 

example/README

@@ -66,5 +66,16 @@ Code review:
       - Real use cases are likely to use more sophisticated select-script
         callbacks (e.g., to select from a range of changelists).
 
+      - The example uses caching and profile history to improve runtime
+        performance - see the man pages for a more detailed description
+        of the features.  There is no effect with a tiny example - but
+        a real project may see benefit.
+        The 'spreadsheet.py' application script can be used to convert
+        JSON profile files into more readable excel spreadsheets.  This
+        can be useful to see the effect (if any) of the caching and/or
+        history features, and can show where time is spent for your example.
+        This can be helpful, to suggest opportunities to optimize the LCOV
+        implementation.
+
 Feel free to edit the Makefile or to run the lcov utilities directly,
 to see the effect of other options that you find in the lcov man pages.