[PATCH] Cygwin: Speed up mkimport

[Mark Geisert]

Cut mkimport elapsed time in half by forking each iteration of the two
time-consuming loops within.  Only do this if more than one CPU is
present.  In the second loop, combine the two 'objdump' calls into one
system() invocation to avoid a system() invocation per iteration.

---
 winsup/cygwin/mkimport | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/winsup/cygwin/mkimport b/winsup/cygwin/mkimport
index 2b08dfe3d..919dc305b 100755
--- a/winsup/cygwin/mkimport
+++ b/winsup/cygwin/mkimport
@@ -47,6 +47,9 @@ for my $sym (keys %replace) {
     $import{$fn} = $imp_sym;
 }
 
+my $ncpus = `grep -c ^processor /proc/cpuinfo`;
+my $forking = $ncpus > 1; # Decides if loops below should fork() each iteration
+
 for my $f (keys %text) {
     my $imp_sym = delete $import{$f};
     my $glob_sym = $text{$f};
@@ -56,25 +59,30 @@ for my $f (keys %text) {
        $text{$f} = 0;
     } else {
        $text{$f} = 1;
-       open my $as_fd, '|-', $as, '-o', "$dir/t-$f", "-";
-       if ($is64bit) {
-           print $as_fd <<EOF;
+       if ($forking && fork) {
+           ; # Testing shows sleep here is unneeded. 'as' runs very quickly.
+       } else {
+           open my $as_fd, '|-', $as, '-o', "$dir/t-$f", "-";
+           if ($is64bit) {
+               print $as_fd <<EOF;
        .text
        .extern $imp_sym
        .global $glob_sym
 $glob_sym:
        jmp     *$imp_sym(%rip)
 EOF
-       } else {
-           print $as_fd <<EOF;
+           } else {
+               print $as_fd <<EOF;
        .text
        .extern $imp_sym
        .global $glob_sym
 $glob_sym:
        jmp     *$imp_sym
 EOF
+           }
+           close $as_fd or exit 1;
+           exit 0 if $forking;
        }
-       close $as_fd or exit 1;
     }
 }
 
@@ -86,8 +94,18 @@ for my $f (keys %text) {
     if (!$text{$f}) {
        unlink $f;
     } else {
-       system $objcopy, '-R', '.text', $f and exit 1;
-       system $objcopy, '-R', '.bss', '-R', '.data', "t-$f" and exit 1;
+       if ($forking && fork) {
+           # Testing shows parent does need to sleep a short time here,
+           # otherwise system is inundated with hundreds of objcopy processes
+           # and the forked perl processes that launched them.
+           my $delay = 0.01; # NOTE: Slower systems may need to raise this
+           select(undef, undef, undef, $delay); # Supports fractional seconds
+       } else {
+           # Do two objcopy calls at once to avoid one system() call overhead
+           system '(', $objcopy, '-R', '.text', $f, ')', '||',
+               $objcopy, '-R', '.bss', '-R', '.data', "t-$f" and exit 1;
+           exit 0 if $forking;
+       }
     }
 }
 
-- 
2.29.2