[committed] Do finalize-multifile in parallel

[committed] Do finalize-multifile in parallel

[Tom de Vries]

Hi,

Run the finalize-multifile phase in parallel.

Using an experiment, we can see the effect:
...
$ for j in $(seq 1 2); do \
    rm -f 1 2 3; \
    cp debug/cc1 1; cp 1 2; \
    echo "j: $j"; \
    ../measure/time.sh ./dwz -lnone -m 3 1 2 -j$j; \
  done
j: 1
maxmem: 1295068
real: 26.38
user: 25.38
system: 0.77
j: 2
maxmem: 1297724
real: 23.55
user: 25.81
system: 0.88
...

Committed to trunk.

Thanks,
- Tom

Do finalize-multifile in parallel

2021-03-27  Tom de Vries  <tdevries@suse.de>

	* dwz.c (dwz_files_1): Run finalize-multifile phase in parallel, if
	max_forks > 0.

---
 dwz.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 62 insertions(+), 14 deletions(-)

diff --git a/dwz.c b/dwz.c
index 3cc0a26..eeae750 100644
--- a/dwz.c
+++ b/dwz.c
@@ -16608,21 +16608,69 @@ dwz_files_1 (int nr_files, char *files[], bool hardlink,
       goto cleanup;
     }
 
-  for (i = 0; i < nr_files; i++)
+  if (max_forks > 1)
     {
-      dw_cu_ref cu;
-      file = files[i];
-      if (stats_p)
-	init_stats (file);
-      multifile_mode = MULTIFILE_MODE_FI;
-      /* Don't process again files that couldn't
-	 be processed successfully.  Also skip hard links.  */
-      if (resa[i].res == -1 || resa[i].res == -2
-	  || resa[i].skip_multifile)
-	continue;
-      for (cu = alt_first_cu; cu; cu = cu->cu_next)
-	alt_clear_dups (cu->cu_die);
-      ret |= dwz (file, NULL, &resa[i]);
+      pid_t pids[nr_files];
+      int nr_forks = 0;
+      for (i = 0; i < nr_files; i++)
+	pids[i] = 0;
+      for (i = 0; i < nr_files; i++)
+	{
+	  file = files[i];
+	  struct file_result *res = &resa[i];
+	  multifile_mode = MULTIFILE_MODE_FI;
+	  /* Don't process again files that couldn't
+	     be processed successfully.  Also skip hard links.  */
+	  if (resa[i].res == -1 || resa[i].res == -2
+	      || resa[i].skip_multifile)
+	    continue;
+
+	  if (nr_forks == max_forks)
+	    {
+	      int thisret = wait_child_exit (-1, pids, i, res);
+	      if (thisret == 1)
+		ret = 1;
+	      nr_forks--;
+	    }
+
+	  pid_t fork_res = fork ();
+	  assert (fork_res != -1);
+	  if (fork_res == 0)
+	    {
+	      int thisret = dwz (file, NULL, res);
+	      return encode_child_exit_status (thisret, res);
+	    }
+	  else
+	    {
+	      pids[i] = fork_res;
+	      nr_forks++;
+	    }
+	}
+      if (nr_forks > 0)
+	{
+	  int thisret = wait_children_exit (pids, nr_files, resa);
+	  if (thisret == 1)
+	    ret = 1;
+	}
+    }
+  else
+    {
+      for (i = 0; i < nr_files; i++)
+	{
+	  dw_cu_ref cu;
+	  file = files[i];
+	  if (stats_p)
+	    init_stats (file);
+	  multifile_mode = MULTIFILE_MODE_FI;
+	  /* Don't process again files that couldn't
+	     be processed successfully.  Also skip hard links.  */
+	  if (resa[i].res == -1 || resa[i].res == -2
+	      || resa[i].skip_multifile)
+	    continue;
+	  for (cu = alt_first_cu; cu; cu = cu->cu_next)
+	    alt_clear_dups (cu->cu_die);
+	  ret |= dwz (file, NULL, &resa[i]);
+	}
     }
 
   if (hardlink)