This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [RFC] Old school parallelization of WPA streaming


Hi,
I am not sure where we converged concerning the fork trick.  I am using it in my
tree for months and it does save my waiting time for WPA compilations, so I am
re-attaching the patch.

Does it seem resonable for mainline?

As for other plans mentioned on this thread
> > 
> > I still have some items on list here
> >  1) avoid function sections to be decompressed by WPA
> >     (this won't cause much compile time improvements as decompression is
> >      well bellow 10% of runtime)
> 
> still low-hanging
> 
> finally get a LTO section header!  (with a flag telling whether the
> section is compressed)

I have patch for it somewhere (not particularly clean, we need to dig more into
the basic section handling code in LTO). The benefits however was quite small
(we get dominated by decls and types still), so perhaps this can wait for next
stage1 or a development branch.
> 
> >  2) put variable initializers into named sections just as function bodies
> >     are.
> >     Seeing Martin's systemtaps of firefox/gimp/inkscape, to my surprise the
> >     initializers are actually about as big as the text segment.  While
> >     it seems bit wasteful to pust single integer_cst there (and we can
> >     special case this), it seems that there is a promise for vtables
> >     and other stuff.
> > 
> >     To make devirt work, we will need to load vtables into memory (or
> >     invent representation to stream them other way that would be similarly
> >     big). Still we will avoid need to load them in 5000 copies and merge
> >     them.

Did not fnish this, unfortunately (devirtualization was more involved and
I lost track on this one).  I had a prototype working where savings was about
15% of WPA memory.  I will try to get cleaner implementation soon.

> >  3) I think good part of function/partitioning overhead is because abstract
> >     origin streaming is utterly broken.

Yep, this is definitely still in longer term plans only.

Honza

	* lto-cgraph.c (asm_nodes_output): Make global.
	* lto-streamer.h (asm_nodes_output): Declare.
	* lto-wrapper.c (parallel, jobserver): Make global.
	(run_gcc): Pass down -fparallelism

	* lto.c (lto_parallelism): New variable.
	(do_stream_out): New function.
	(stream_out): New function.
	(lto_wpa_write_files): Use it.
	* lang.opt (fparallelism): New.
	* lto.h (lto_parallelism): Declare.
	* lto-lang.c (lto_handle_option): Add fparalelism.

Index: lto-cgraph.c
===================================================================
--- lto-cgraph.c	(revision 201891)
+++ lto-cgraph.c	(working copy)
@@ -50,6 +50,9 @@ along with GCC; see the file COPYING3.
 #include "context.h"
 #include "pass_manager.h"
 
+/* True when asm nodes has been output.  */
+bool asm_nodes_output = false;
+
 static void output_cgraph_opt_summary (void);
 static void input_cgraph_opt_summary (vec<symtab_node>  nodes);
 
@@ -852,7 +855,6 @@ output_symtab (void)
   lto_symtab_encoder_iterator lsei;
   int i, n_nodes;
   lto_symtab_encoder_t encoder;
-  static bool asm_nodes_output = false;
 
   if (flag_wpa)
     output_cgraph_opt_summary ();
Index: lto-streamer.h
===================================================================
--- lto-streamer.h	(revision 201891)
+++ lto-streamer.h	(working copy)
@@ -870,6 +870,7 @@ void lto_output_location (struct output_
 
 
 /* In lto-cgraph.c  */
+extern bool asm_nodes_output;
 lto_symtab_encoder_t lto_symtab_encoder_new (bool);
 int lto_symtab_encoder_encode (lto_symtab_encoder_t, symtab_node);
 void lto_symtab_encoder_delete (lto_symtab_encoder_t);
Index: lto-wrapper.c
===================================================================
--- lto-wrapper.c	(revision 201891)
+++ lto-wrapper.c	(working copy)
@@ -56,6 +56,9 @@ along with GCC; see the file COPYING3.
 
 int debug;				/* true if -save-temps.  */
 int verbose;				/* true if -v.  */
+int parallel = 0;			/* number of parallel builds specified
+					   by -flto=N  */
+int jobserver = 0;			/* true if -flto=jobserver was used.  */
 
 enum lto_mode_d {
   LTO_MODE_NONE,			/* Not doing LTO.  */
@@ -445,8 +448,6 @@ run_gcc (unsigned argc, char *argv[])
   char *list_option_full = NULL;
   const char *linker_output = NULL;
   const char *collect_gcc, *collect_gcc_options;
-  int parallel = 0;
-  int jobserver = 0;
   bool no_partition = false;
   struct cl_decoded_option *fdecoded_options = NULL;
   unsigned int fdecoded_options_count = 0;
@@ -630,6 +631,16 @@ run_gcc (unsigned argc, char *argv[])
 	      if (parallel <= 1)
 		parallel = 0;
 	    }
+	  if (jobserver)
+	    {
+	      obstack_ptr_grow (&argv_obstack, xstrdup ("-fparallelism=jobserver"));
+	    }
+	  else if (parallel > 1)
+	    {
+	      char buf[256];
+	      sprintf (buf, "-fparallelism=%i", parallel);
+	      obstack_ptr_grow (&argv_obstack, xstrdup (buf));
+	    }
 	  /* Fallthru.  */
 
 	case OPT_flto:
Index: lto/lto.c
===================================================================
--- lto/lto.c	(revision 201891)
+++ lto/lto.c	(working copy)
@@ -49,6 +49,9 @@ along with GCC; see the file COPYING3.
 #include "context.h"
 #include "pass_manager.h"
 
+/* Number of parallel tasks to run, -1 if we want to use GNU Make jobserver.  */
+int lto_parallelism;
+
 static GTY(()) tree first_personality_decl;
 
 /* Returns a hash code for P.  */
@@ -3002,6 +3005,98 @@ cmp_partitions_order (const void *a, con
   return orderb - ordera;
 }
 
+/* Actually stream out ENCODER into TEMP_FILENAME.  */
+
+void
+do_stream_out (char *temp_filename, lto_symtab_encoder_t encoder)
+{
+  lto_file *file = lto_obj_file_open (temp_filename, true);
+  if (!file)
+    fatal_error ("lto_obj_file_open() failed");
+  lto_set_current_out_file (file);
+
+  ipa_write_optimization_summaries (encoder);
+
+  lto_set_current_out_file (NULL);
+  lto_obj_file_close (file);
+  free (file);
+}
+
+/* Wait for forked process and signal errors.  */
+#ifdef HAVE_WORKING_FORK
+void
+wait_for_child ()
+{
+  int status;
+  do
+    {
+      int w = waitpid(0, &status, WUNTRACED | WCONTINUED);
+      if (w == -1)
+	fatal_error ("waitpid failed");
+
+      if (WIFEXITED (status) && WEXITSTATUS (status))
+	fatal_error ("streaming subprocess failed");
+      else if (WIFSIGNALED (status))
+	fatal_error ("streaming subprocess was killed by signal");
+    }
+  while (!WIFEXITED(status) && !WIFSIGNALED(status));
+}
+#endif
+
+/* Stream out ENCODER into TEMP_FILENAME
+   Fork if that seems to help.  */
+
+void
+stream_out (char *temp_filename, lto_symtab_encoder_t encoder, bool last)
+{
+#ifdef HAVE_WORKING_FORK
+  static int nruns;
+
+  if (!lto_parallelism || lto_parallelism == 1)
+    {
+      do_stream_out (temp_filename, encoder);
+      return;
+    }
+
+  /* Do not run more than LTO_PARALLELISM streamings
+     FIXME: we ignore limits on jobserver.  */
+  if (lto_parallelism > 0 && nruns >= lto_parallelism)
+    {
+      wait_for_child ();
+      nruns --;
+    }
+  /* If this is not the last parallel partition, execute new
+     streaming process.  */
+  if (!last)
+    {
+      pid_t cpid = fork ();
+
+      if (!cpid)
+	{
+	  setproctitle ("lto1-wpa-streaming");
+	  do_stream_out (temp_filename, encoder);
+	  exit (0);
+	}
+      /* Fork failed; lets do the job ourseleves.  */
+      else if (cpid == -1)
+        do_stream_out (temp_filename, encoder);
+      else
+	nruns++;
+    }
+  /* Last partition; stream it and wait for all children to die.  */
+  else
+    {
+      int i;
+      do_stream_out (temp_filename, encoder);
+      for (i = 0; i < nruns; i++)
+	wait_for_child ();
+    }
+  asm_nodes_output = true;
+#else
+  do_stream_out (temp_filename, encoder);
+#endif
+}
+
 /* Write all output files in WPA mode and the file with the list of
    LTRANS units.  */
 
@@ -3009,18 +3104,15 @@ static void
 lto_wpa_write_files (void)
 {
   unsigned i, n_sets;
-  lto_file *file;
   ltrans_partition part;
   FILE *ltrans_output_list_stream;
   char *temp_filename;
+  vec <char *>temp_filenames = vNULL;
   size_t blen;
 
   /* Open the LTRANS output list.  */
   if (!ltrans_output_list)
     fatal_error ("no LTRANS output list filename provided");
-  ltrans_output_list_stream = fopen (ltrans_output_list, "w");
-  if (ltrans_output_list_stream == NULL)
-    fatal_error ("opening LTRANS output list %s: %m", ltrans_output_list);
 
   timevar_push (TV_WHOPR_WPA);
 
@@ -3056,14 +3148,10 @@ lto_wpa_write_files (void)
 			   : cmp_partitions_order);
   for (i = 0; i < n_sets; i++)
     {
-      size_t len;
       ltrans_partition part = ltrans_partitions[i];
 
       /* Write all the nodes in SET.  */
       sprintf (temp_filename + blen, "%u.o", i);
-      file = lto_obj_file_open (temp_filename, true);
-      if (!file)
-	fatal_error ("lto_obj_file_open() failed");
 
       if (!quiet_flag)
 	fprintf (stderr, " %s (%s %i insns)", temp_filename, part->name, part->insns);
@@ -3105,21 +3193,25 @@ lto_wpa_write_files (void)
 	}
       gcc_checking_assert (lto_symtab_encoder_size (part->encoder) || !i);
 
-      lto_set_current_out_file (file);
-
-      ipa_write_optimization_summaries (part->encoder);
+      stream_out (temp_filename, part->encoder, i == n_sets - 1);
 
-      lto_set_current_out_file (NULL);
-      lto_obj_file_close (file);
-      free (file);
       part->encoder = NULL;
 
-      len = strlen (temp_filename);
-      if (fwrite (temp_filename, 1, len, ltrans_output_list_stream) < len
+      temp_filenames.safe_push (xstrdup (temp_filename));
+    }
+  ltrans_output_list_stream = fopen (ltrans_output_list, "w");
+  if (ltrans_output_list_stream == NULL)
+    fatal_error ("opening LTRANS output list %s: %m", ltrans_output_list);
+  for (i = 0; i < n_sets; i++)
+    {
+      unsigned int len = strlen (temp_filenames[i]);
+      if (fwrite (temp_filenames[i], 1, len, ltrans_output_list_stream) < len
 	  || fwrite ("\n", 1, 1, ltrans_output_list_stream) < 1)
 	fatal_error ("writing to LTRANS output list %s: %m",
 		     ltrans_output_list);
+     free (temp_filenames[i]);
     }
+  temp_filenames.release();
 
   lto_stats.num_output_files += n_sets;
 
Index: lto/lang.opt
===================================================================
--- lto/lang.opt	(revision 201891)
+++ lto/lang.opt	(working copy)
@@ -32,6 +32,10 @@ fltrans-output-list=
 LTO Joined Var(ltrans_output_list)
 Specify a file to which a list of files output by LTRANS is written.
 
+fparallelism=
+LTO Joined
+Run the link-time optimizer in whole program analysis (WPA) mode.
+
 fwpa
 LTO Driver Report Var(flag_wpa)
 Run the link-time optimizer in whole program analysis (WPA) mode.
Index: lto/lto.h
===================================================================
--- lto/lto.h	(revision 201891)
+++ lto/lto.h	(working copy)
@@ -39,6 +39,7 @@ extern const char *resolution_file_name;
 extern tree lto_eh_personality (void);
 extern void lto_main (void);
 extern void lto_read_all_file_options (void);
+extern int lto_parallelism;
 
 /* In lto-elf.c or lto-coff.c  */
 extern lto_file *lto_obj_file_open (const char *filename, bool writable);
Index: lto/lto-lang.c
===================================================================
--- lto/lto-lang.c	(revision 201891)
+++ lto/lto-lang.c	(working copy)
@@ -735,6 +735,19 @@ lto_handle_option (size_t scode, const c
       warn_psabi = value;
       break;
 
+    case OPT_fparallelism_:
+      if (!arg)
+	lto_parallelism = 1;
+      else if (!strcmp (arg, "jobserver"))
+	lto_parallelism = -1;
+      else
+	{
+	  lto_parallelism = atoi (arg);
+	  if (lto_parallelism <= 0)
+	    lto_parallelism = 0;
+	}
+      break;
+
     default:
       break;
     }


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]