On Thu, 21 Nov 2013, Jan Hubicka wrote:
> 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.
Why do you need an additional -fparallelism? Wouldn't
-fwpa=... be a better match, matching -flto=...? As we already
pass down a -fwpa option to WPA this would make things easier, no?
Thanks,
Richard.
> 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;
> }
>
>
--
Richard Biener <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend"orffer
