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Date:      Fri, 29 Jun 2012 13:16:47 -0700
From:      Yuri <yuri@rawbw.com>
To:        freebsd-hackers@FreeBSD.org
Subject:   System is flooded with failed read(2) calls: Resource temporarily unavailable (errno=35) coming from xorg unix socket
Message-ID:  <4FEE0D2F.4010808@rawbw.com>
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When I run dtrace script (attached) on 9.0 amd64 with kde4 I see a lot 
of failed read(2) calls from the xorg socket /tmp/.X11-unix/X0 .
This can't be right in my opinion. This means that code keeps reading 
from this socket and failing, instead of using select(2) or kquere(2).
Requests mostly come from kdeinit4 but some also from kwin, chrome and 
even Xorg itself.
Rate of failure for read(2) calls is ~2500/sec systemwide.

This is of course not a deadly problem.
But is this situation considered to be normal?

Yuri

--- dtrace script---
!/usr/bin/perl
use Getopt::Std;

#
#  Defaults
#
$FILTER = "";
$COUNT = 0;

#
#  Command line arguments
#
&Usage() if $ARGV[0] eq "--help";
getopts('ch:n:p:') || &Usage();
&Usage() if $opt_h;
$COUNT = 1 if $opt_c;
$FILTER = "&& execname == \"$opt_n\"" if defined $opt_n;
$FILTER = "&& pid == $opt_p" if defined $opt_p;

#
#  Load errno descriptions
#
open(ERRNO,"/usr/include/sys/errno.h") || die "ERROR1: reading errno.h: 
$!\n";
while (chomp($line = <ERRNO>)) {
         next unless $line =~ /^#define/;
         ($errno,$desc) = $line =~ /^#define\s+\S+\s+(\d+)\s+\/\*(.*)\*\//;
         $Errno{$errno} = $desc;
}
close ERRNO;

#
#  Declare DTrace script
#
  if ($COUNT) {          # aggregate style
$dtrace = <<END;
/usr/sbin/dtrace -n '
         #pragma D option quiet
         syscall:::return
         /errno != 0 && pid != \$pid $FILTER/
         {
                 \@Errs[execname, probefunc, errno] = count();
         }
         dtrace:::END {
                 printa("%s %s %d %\@d\\n", \@Errs);
         }'
END
  } else {               # snoop style
$dtrace = <<END;
/usr/sbin/dtrace -n '
         #pragma D option quiet
         #pragma D option switchrate=5hz
         syscall::read:entry
         {
           self->fd = arg0;
         }
         syscall::read:return
         /errno != 0 && pid != \$pid $FILTER/
         {
                 printf("%d %s %s %d\\n", pid, execname, probefunc, errno);
                 printf("fd=%d\\n",self->fd);
         }'
END
  }

#
#  Cleanup on signals
#
$SIG{INT} = \&Cleanup_Signal;    # Ctrl-C
$SIG{QUIT} = \&Cleanup_Signal;   # Ctrl-\
$SIG{TERM} = \&Cleanup_Signal;   # TERM

#
#  Run DTrace, process output
#

if ($COUNT) {
         print STDERR "Sampling... Hit Ctrl-C to end.\n";
         $header = 1;
} else {
         printf("%16s %16s %4s  %s\n","EXEC","SYSCALL","ERR","DESC");
}

### Open DTrace
open(DTRACE,"$dtrace |") || die "ERROR2: Can't start dtrace (perms?): $!\n";

### Process DTrace output
while (chomp($line = <DTRACE>)) {

         ### Print count header
         if ($COUNT && $header) {
                 printf("\n%16s %16s %16s %4s %6s  %s\n",
                  "PID", "EXEC","SYSCALL","ERR","COUNT","DESC");
                 $header = 0;
         }

         ### Split data
         ($pid,$execname,$syscall,$errno,$counts) = split(' ',$line);
         if ($errno eq "") {printf("DESCR %s\n", $line);}
         next if $errno eq "";

         ### Fetch errno description
         $desc = $Errno{$errno};

         ### Print output line
         if ($COUNT) {
                 printf("%16s %16s %16s %4d %6d %s\n",
                  $pid, $execname,$syscall,$errno,$counts,$desc);
         } else {
                 printf("%16s %16s %16s %4d 
%s\n",$pid,$execname,$syscall,$errno,$desc);
         }
}
close(DTRACE);

#
#  Triggered by signals
#
sub Cleanup_Signal {
}

#
#  Usage message
#
sub Usage {
         print STDERR "USAGE: errinfo [-ch] [-p PID] [-n name]\n";
         print STDERR <<ENDUSAGE;
      eg,
        errinfo       # default output - snoop event style
           -c         # counts - aggregate style
           -p 871     # examine PID 871 only
           -n ssh     # examine processes with the name "ssh" only
           -cn ssh    # examine "ssh" using counts
ENDUSAGE
         exit(1);
}

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