GCC Summit 2010

GCC Summit 2010 slides are available at
http://gcc.gnu.org/wiki/summit2010

top failed ro read /proc/stat

Just noticed that top utiliy fails to read /proc/stat after
cpu offline.

The problem is that Cpu_tot is not updated before calling
cpus_refresh.

In cpus_refresh we're trying to read and sscanf Cpu_tot times /proc/stat

   for (i = 0; 1 < Cpu_tot && i < Cpu_tot; i++) {
      if (!fgets(buf, sizeof(buf), fp)) std_err("failed /proc/stat read");
      cpus[i].x = 0;  // FIXME: can't tell by kernel version number
      cpus[i].y = 0;  // FIXME: can't tell by kernel version number
      cpus[i].z = 0;  // FIXME: can't tell by kernel version number
      num = sscanf(buf, "cpu%u %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu",
         &cpus[i].id,
         &cpus[i].u, &cpus[i].n, &cpus[i].s, &cpus[i].i, &cpus[i].w, &cpus[i].x, &cpus[i].y, &cpus[i].z
      );
      if (num < 4)
          std_err("failed /proc/stat read");
   }

Which is wrong, since:
cat /proc/stat
cpu  5700 0 1474 271836 3554 0 41 0 0 0
cpu0 2167 0 565 66945 974 0 13 0 0 0
cpu1 2600 0 507 66512 1030 0 11 0 0 0
cpu2 518 0 214 69082 810 0 5 0 0 0
cpu3 413 0 186 69296 738 0 9 0 0 0
intr ....

echo 0 > /sys/devices/system/cpu/cpu3/online
cat /proc/stat
cpu  5831 0 1531 292475 3592 0 43 0 0 0
cpu0 2236 0 591 72477 979 0 14 0 0 0
cpu1 2647 0 531 72052 1051 0 12 0 0 0
cpu2 527 0 217 74713 821 0 6 0 0 0
intr ...

(note absent cpu3 line).


The solution may look similar to this one:

      smp_num_cpus = sysconf(_SC_NPROCESSORS_ONLN);
      if(smp_num_cpus<1) smp_num_cpus=1;
      Cpu_tot = smp_num_cpus;

Before cpus_refresh call.

Mutt 1.5.21 mail_check_recent option

Updated to mutt 1.5.21 recently and one change really was annoying me so far.
Mutt doesn't mark recently visited folder with 'N' (new message) until it
receives new message... even if there are unread messages.
Quick look at mutt 1.5.21 source code gave the following result:

/* returns 1 if maildir has new mail */
static int buffy_maildir_hasnew (BUFFY* mailbox)
{
  char path[_POSIX_PATH_MAX];
  DIR *dirp;
  struct dirent *de;
  char *p;
  int rc = 0;
  struct stat sb;

  snprintf (path, sizeof (path), "%s/new", mailbox->path);

  /* when $mail_check_recent is set, if the new/ directory hasn't been modified since
   * the user last exited the mailbox, then we know there is no recent mail.
   */
  if (option(OPTMAILCHECKRECENT))
  {
    if (stat(path, &sb) == 0 && sb.st_mtime < mailbox->last_visited)
      return 0;
  }

  if ((dirp = opendir (path)) == NULL)
  {
    mailbox->magic = 0;
    return 0;
  }

  while ((de = readdir (dirp)) != NULL)
  {
    if (*de->d_name == '.')
      continue;

    if (!(p = strstr (de->d_name, ":2,")) || !strchr (p + 3, 'T'))
    {
      if (option(OPTMAILCHECKRECENT))
      {
    char msgpath[_POSIX_PATH_MAX];

    snprintf(msgpath, sizeof(msgpath), "%s/%s", path, de->d_name);
    /* ensure this message was received since leaving this mailbox */
    if (stat(msgpath, &sb) == 0 && (sb.st_ctime <= mailbox->last_visited))
      continue;
      }
      /* one new and undeleted message is enough */
      mailbox->new = 1;
      rc = 1;
      break;
    }
  }

  closedir (dirp);

  return rc;
}

Gotcha! Quick grep:

{"mail_check_recent",DT_BOOL, R_NONE, OPTMAILCHECKRECENT, 1 },
When set, Mutt will only notify you about new mail that has been received
since the last time you opened the mailbox.  When unset, Mutt will notify
you if any new mail exists in the mailbox, regardless of whether you have
visited it recently.

Corresponding lines in change log (diff 1.5.20 - 1.5.21)

2010-09-13 17:25 -0700  Michael Elkins (20b2d496349f)
* init.h: make $mail_check_recent set by default

The solution is to add
unset mail_check_recent

to .muttrc


Why...

Glibc: moving forward to gcc-4.6

Glibc: moving forward to gcc-4.6

Author: Ulrich Drepper
Date:   Tue Oct 19 12:56:42 2010 -0400

    Provide FP_FAST_FMA{,F,L} definitions for x86/x86-64.

diff --git a/sysdeps/x86_64/bits/mathdef.h b/sysdeps/x86_64/bits/mathdef.h
index 7b16189..9146392 100644
--- a/sysdeps/x86_64/bits/mathdef.h
+++ b/sysdeps/x86_64/bits/mathdef.h
[..]

+/* The GCC 4.6 compiler will define __FP_FAST_FMA{,F,L} if the fma{,f,l}
+   builtins are supported.  */
+# if __FP_FAST_FMA
+#  define FP_FAST_FMA 1
+# endif
+
+# if __FP_FAST_FMAF
+#  define FP_FAST_FMAF 1
+# endif
+
+# if __FP_FAST_FMAL
+#  define FP_FAST_FMAL 1
+# endif
+
 #endif /* ISO C99 */

http://www.linuxselfhelp.com/gnu/glibc/html_chapter/libc_20.html

On processors which do not implement multiply-add in hardware, fma can be very slow since it must avoid intermediate rounding. `math.h' defines the symbols FP_FAST_FMA, FP_FAST_FMAF, and FP_FAST_FMAL when the corresponding version of fma is no slower than the expression `x*y + z'. In the GNU C library, this always means the operation is implemented in hardware.

wired: "Oct. 14, 1985: C++ Adds to Programming"

Interview with Bjarne Stroustrup (C++ is 25... a bit outdated).

Wired.com: Most programmers are particular about the music they listen to while coding or writing. What do you listen to?

Stroustrup: Tchaikovsky’s Fifth, Wagner’s The Ring Without Words, Grieg’s Peer Gynt Suite, Sibelius, Nielsen’s The Inextinguishable, various Mozart concertos, The Dixie Chicks, Beatles’ Abbey Road, Handel’s Messiah and Water Music, Eric Clapton, Beethoven’s Fifth and Seventh. I looked to see what my laptop had been playing lately.

...

Wired.com: Any advice for young programmers?

Stroustrup: I guess giving advice is easy compared to taking it. Know your fundamentals (algorithms, data structures, machine architecture, systems) and know several programming languages to the point where you can use them idiomatically.

Know some non-computer field of study well — math, biology, history, optics, whatever. Learn to communicate effectively in speech and in writing. Spend an unreasonable amount of time on some difficult topic to really master it. Try to do something that might make a difference in the world.

Full story via wired.com

www.☭.net

Just for note: Unicode 6.0 has been released.

www.☭.net

10/10/10

101010 == 42 - The Answer to Life, The Universe, and Everything.