src/readelf.c: Support concurrency for -w, --debug-dump

Implement concurrent execution of print_debug_* functions during handling
of -w, --debug-dump using libthread.a.

A new `-C, --concurrency=NUM` command line option controls the maximum
number of threads that may be used. This value defaults to the number of CPUs.

Job output is buffered and printed in the order that jobs were added to
the queue. This helps preserve the existing order of stdout output. Full
support for output buffering in print_debug_* functions is added in the
next patch in this series.

	* src/readelf.c (default_concurrency): Function estimating the
	maximum number of threads.
	(parse_opt): Handle -C, --concurrency=NUM.
	(do_job): Entry point function for threads.
	(schedule_job): If thread safety is enabled, add job to the
	job queue.  Otherwise just run the job from the main thread.
	(print_debug): Pass print_debug_* function pointers and
	args to schedule_job. Also call run_jobs if thread safety
	is enabled.

Signed-off-by: Aaron Merey <amerey@redhat.com>
v3:
Replace assert before run_jobs with a conditional.

diff --git a/src/readelf.c b/src/readelf.c
index b7dba390e4fb1b903b8b71435240f370927a5d9a..e3aece8b5b9945d1e303f62f956e870c258c7a82 100644 (file)
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -57,6 +57,18 @@
 
 #include "../libdw/known-dwarf.h"
 
+#ifdef USE_LOCKS
+#include "threadlib.h"
+#endif
+
+#ifdef HAVE_SCHED_H
+#include <sched.h>
+#endif
+
+#ifdef HAVE_SYS_RESOURCE_H
+#include <sys/resource.h>
+#endif
+
 #ifdef __linux__
 #define CORE_SIGILL  SIGILL
 #define CORE_SIGBUS  SIGBUS
@@ -150,6 +162,10 @@ static const struct argp_option options[] =
     N_("Ignored for compatibility (lines always wide)"), 0 },
   { "decompress", 'z', NULL, 0,
     N_("Show compression information for compressed sections (when used with -S); decompress section before dumping data (when used with -p or -x)"), 0 },
+#ifdef USE_LOCKS
+  { "concurrency", 'C', "NUM", 0,
+    N_("Set maximum number of threads. Defaults to the number of CPUs."), 0 },
+#endif
   { NULL, 0, NULL, 0, NULL, 0 }
 };
 
@@ -249,6 +265,11 @@ static bool print_decompress = false;
 /* True if we want to show split compile units for debug_info skeletons.  */
 static bool show_split_units = false;
 
+#if USE_LOCKS
+/* Maximum number of threads.  */
+static int max_threads = -1;
+#endif
+
 /* Select printing of debugging sections.  */
 static enum section_e
 {
@@ -380,6 +401,43 @@ cleanup_list (struct section_argument *list)
     }
 }
 
+#ifdef USE_LOCKS
+/* Estimate the maximum number of threads. This is normally
+   #CPU.  Return value is guaranteed to be at least 1.  */
+static int
+default_concurrency (void)
+{
+  unsigned aff = 0;
+#ifdef HAVE_SCHED_GETAFFINITY
+  {
+    int ret;
+    cpu_set_t mask;
+    CPU_ZERO (&mask);
+    ret = sched_getaffinity (0, sizeof(mask), &mask);
+    if (ret == 0)
+      aff = CPU_COUNT (&mask);
+  }
+#endif
+
+  unsigned fn = 0;
+#ifdef HAVE_GETRLIMIT
+  {
+    struct rlimit rlim;
+    int rc = getrlimit (RLIMIT_NOFILE, &rlim);
+    if (rc == 0)
+      fn = MAX ((rlim_t) 1, (rlim.rlim_cur - 100) / 2);
+    /* Conservatively estimate that at least 2 fds are used
+       by each thread.  */
+  }
+#endif
+
+  unsigned d = MIN (MAX (aff, 2U),
+                   MAX (fn, 2U));
+
+  return d;
+}
+#endif
+
 int
 main (int argc, char *argv[])
 {
@@ -403,6 +461,12 @@ main (int argc, char *argv[])
   /* Before we start tell the ELF library which version we are using.  */
   elf_version (EV_CURRENT);
 
+#ifdef USE_LOCKS
+  /* If concurrency wasn't set by argp_parse, then set a default value.  */
+  if (max_threads == -1)
+    max_threads = default_concurrency ();
+#endif
+
   /* Now process all the files given at the command line.  */
   bool only_one = remaining + 1 == argc;
   do
@@ -527,6 +591,16 @@ parse_opt (int key, char *arg,
     case 'c':
       print_archive_index = true;
       break;
+#if USE_LOCKS
+    case 'C':
+      if (arg != NULL)
+       {
+         max_threads = atoi (arg);
+         if (max_threads < 1)
+           error (1, 0, _("-C NUM minimum 1"));
+       }
+      break;
+#endif
     case 'w':
       if (arg == NULL)
        {
@@ -5492,7 +5566,7 @@ listptr_base (struct listptr *p)
 }
 
 /* To store the name used in compare_listptr */
-static const char *sort_listptr_name;
+_Thread_local const char *sort_listptr_name;
 
 static int
 compare_listptr (const void *a, const void *b)
@@ -11950,6 +12024,65 @@ getone_dwflmod (Dwfl_Module *dwflmod,
   return DWARF_CB_OK;
 }
 
+typedef struct {
+  Dwfl_Module *dwflmod;
+  Ebl *ebl;
+  GElf_Ehdr *ehdr;
+  Elf_Scn scn;
+  GElf_Shdr shdr;
+  Dwarf *dbg;
+  FILE *out;
+  void (*fp) (Dwfl_Module *, Ebl *, GElf_Ehdr *,
+              Elf_Scn *, GElf_Shdr *, Dwarf *, FILE *);
+} job_data;
+
+#ifdef USE_LOCKS
+
+/* Thread entry point.  */
+static void *
+do_job (void *data, FILE *out)
+{
+  job_data *d = (job_data *) data;
+  d->fp (d->dwflmod, d->ebl, d->ehdr, &d->scn, &d->shdr, d->dbg, out);
+  return NULL;
+}
+#endif
+
+/* If readelf is built with thread safety, then set up JDATA at index IDX
+   and add it to the job queue.
+
+   If thread safety is not supported or the maximum number of threads is set
+   to 1, then immediately call START_ROUTINE with the given arguments.  */
+static void
+schedule_job (job_data jdata[], size_t idx,
+             void (*start_routine) (Dwfl_Module *, Ebl *, GElf_Ehdr *,
+                                    Elf_Scn *, GElf_Shdr *, Dwarf *, FILE *),
+             Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr, Elf_Scn *scn,
+             GElf_Shdr *shdr, Dwarf *dbg)
+{
+#ifdef USE_LOCKS
+  if (max_threads > 1)
+    {
+      /* Add to the job queue.  */
+      jdata[idx].dwflmod = dwflmod;
+      jdata[idx].ebl = ebl;
+      jdata[idx].ehdr = ehdr;
+      jdata[idx].scn = *scn;
+      jdata[idx].shdr = *shdr;
+      jdata[idx].dbg = dbg;
+      jdata[idx].fp = start_routine;
+
+      add_job (do_job, (void *) &jdata[idx]);
+    }
+  else
+    start_routine (dwflmod, ebl, ehdr, scn, shdr, dbg, stdout);
+#else
+  (void) jdata; (void) idx;
+
+  start_routine (dwflmod, ebl, ehdr, scn, shdr, dbg, stdout);
+#endif
+}
+
 static void
 print_debug (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr)
 {
@@ -12122,6 +12255,9 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr)
   if (unlikely (elf_getshdrstrndx (ebl->elf, &shstrndx) < 0))
     error_exit (0, _("cannot get section header string table index"));
 
+  size_t num_jobs = 0;
+  job_data jdata[shnum];
+
   /* If the .debug_info section is listed as implicitly required then
      we must make sure to handle it before handling any other debug
      section.  Various other sections depend on the CU DIEs being
@@ -12239,15 +12375,24 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl, GElf_Ehdr *ehdr)
                      && strcmp (&name[14], debug_sections[n].name) == 0)
 )
                {
-                 if ((print_debug_sections | implicit_debug_sections)
-                     & debug_sections[n].bitmask)
-                   debug_sections[n].fp (dwflmod, ebl, ehdr, scn, shdr, dbg);
+                 if (((print_debug_sections | implicit_debug_sections)
+                      & debug_sections[n].bitmask))
+                   schedule_job (jdata, num_jobs++, debug_sections[n].fp,
+                                 dwflmod, ebl, ehdr, scn, shdr, dbg);
+
+                 assert (num_jobs <= shnum);
                  break;
                }
            }
        }
     }
 
+#ifdef USE_LOCKS
+  /* If max_threads == 1, then jobs were immediately run in schedule_job.  */
+  if (max_threads > 1)
+    run_jobs (max_threads - 1);
+#endif
+
   dwfl_end (skel_dwfl);
   free (skel_name);