This adds a simple perl script for reading two files as produced by
the stackusage script and computing the changes in stack usage. For
example:
$ scripts/stackusage -o /tmp/old.su -- CC=gcc-4.7 -j8 fs/ext4/
$ scripts/stackusage -o /tmp/new.su -- CC=gcc-5.0 -j8 fs/ext4/
$ scripts/stackdelta /tmp/{old,new}.su | sort -k5,5g
shows that gcc 5.0 generally produces less stack-hungry code than gcc
4.7. Obviously, the script can also be used for measuring the effect
of commits, .config tweaks or whatnot.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
scripts/stackdelta | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
create mode 100755 scripts/stackdelta
diff --git a/scripts/stackdelta b/scripts/stackdelta
new file mode 100755
index 000000000000..18417098a378
--- /dev/null
+++ b/scripts/stackdelta
@@ -0,0 +1,55 @@
+#!/usr/bin/perl
+
+# Read two files producesd by the stackusage script, and show the
+# delta between them.
+#
+# Currently, only shows changes for functions listed in both files. We
+# could add an option to show also functions which have vanished or
+# appeared (which would often be due to gcc making other inlining
+# decisions).
+#
+# Another possible option would be a minimum absolute value for the
+# delta.
+
+sub read_stack_usage_file {
+ my %su;
+ my $f = shift;
+ open(my $fh, '<', $f)
+ or die "cannot open $f: $!";
+ while (<$fh>) {
+ chomp;
+ my ($file, $func, $size, $type) = split;
+ # Old versions of gcc (at least 4.7) have an annoying quirk in
+ # that a (static) function whose name has been changed into
+ # for example ext4_find_unwritten_pgoff.isra.11 will show up
+ # in the .su file with a name of just "11". Since such a
+ # numeric suffix is likely to change across different
+ # commits/compilers/.configs or whatever else we're trying to
+ # tweak, we can't really track those functions, so we just
+ # silently skip them.
+ #
+ # Newer gcc (at least 5.0) report the full name, so again,
+ # since the suffix is likely to change, we strip it.
+ next if $func =~ m/^[0-9]+$/;
+ $func =~ s/\..*$//;
+ $su{"${file}\t${func}"} = {size => $size, type => $type};
+ }
+ close($fh);
+ return \%su;
+}
+
+@ARGV == 2
+ or die "usage: $0 <old> <new>";
+
+my $old = read_stack_usage_file($ARGV[0]);
+my $new = read_stack_usage_file($ARGV[1]);
+my @common = grep {exists $new->{$_}} keys %$old;
+print join(",", keys %old) . "\n";
+for (@common) {
+ my $x = $old->{$_}{size};
+ my $y = $new->{$_}{size};
+ my $delta = $y - $x;
+ if ($delta) {
+ printf "%s\t%d\t%d\t%+d\n", $_, $x, $y, $delta;
+ }
+}
--
2.1.3
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