[Bug fortran/16970] New: long write times via NFS

["e-frx at arnone dot de dot unifi dot it" <gcc-bugzilla at gcc dot gnu dot org>]

When a g77-compiled standard FORTRAN77 program writes out a file to an
NFS-mounted remote partition, I/O performance dramatically drops.
Same program, on the same machine, writes out the same file in a very short time
when writing to a local partition.
Once created on the local filesystem, the output file can be written to the
NFS-mounted remote partition in a very short time using cp(1) or mv(1).

This behaviour seems g77-specific, since other [proprietary... :( ] FORTRAN
compilers don't have the same issue.

I reproduced the behaviour with several versions of g77, among with:

$ g77 -v 
g77 version 2.95.4 20011002 (Debian prerelease) (from FSF-g77 version 0.5.25 200
10319 (prerelease))
Driving: g77 -v -c -xf77-version /dev/null -xnone
Reading specs from /usr/lib/gcc-lib/i386-linux/2.95.4/specs
gcc version 2.95.4 20011002 (Debian prerelease)
 /usr/lib/gcc-lib/i386-linux/2.95.4/cpp0 -lang-c -v -D__GNUC__=2 -D__GNUC_MINOR_
_=95 -D__ELF__ -D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(pos
ix) -D_LANGUAGE_FORTRAN -traditional -Acpu(i386) -Amachine(i386) -Di386 -D__i386
 -D__i386__ /dev/null /dev/null
GNU CPP version 2.95.4 20011002 (Debian prerelease) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc-lib/i386-linux/2.95.4/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
 /usr/lib/gcc-lib/i386-linux/2.95.4/../../../../include/g++-3
 /usr/lib/gcc-lib/i386-linux/2.95.4/../../../../i386-linux/include
End of omitted list.
 /usr/lib/gcc-lib/i386-linux/2.95.4/f771 -fnull-version -quiet -dumpbase g77-ver
sion.f -version -fversion -o /tmp/cc7Qj77b.s /dev/null
GNU F77 version 2.95.4 20011002 (Debian prerelease) (i386-linux) compiled by GNU
 C version 2.95.4 20011002 (Debian prerelease).
GNU Fortran Front End version 0.5.25 20010319 (prerelease)
 as -V -Qy -o /tmp/cc6Ymqqe.o /tmp/cc7Qj77b.s
GNU assembler version 2.13.90.0.18 (i386-linux) using BFD version 2.13.90.0.18 2
0030121 Debian GNU/Linux
 ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o /tmp/ccpZKWDe /tmp/cc6Ymqq
e.o /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc-lib/i386-linux/2.95.4/crtbegin.
o -L/usr/lib/gcc-lib/i386-linux/2.95.4 -lg2c -lm -lgcc -lc -lgcc /usr/lib/gcc-li
b/i386-linux/2.95.4/crtend.o /usr/lib/crtn.o
 /tmp/ccpZKWDe
__G77_LIBF77_VERSION__: 0.5.25 20010319 (prerelease)
@(#)LIBF77 VERSION 19990503
__G77_LIBI77_VERSION__: 0.5.25 20010319 (prerelease)
@(#) LIBI77 VERSION pjw,dmg-mods 19990503
__G77_LIBU77_VERSION__: 0.5.25 20010319 (prerelease)
@(#) LIBU77 VERSION 19980709

$ g77 -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/3.2.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --with-system-zlib --enable-__cxa_atexit --host=i386-redhat-linux
Thread model: posix
gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-34)

$ g77-3.3 -v
Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.3/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,objc,ada,treelang --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib
--enable-nls --without-included-gettext --enable-__cxa_atexit
--enable-clocale=gnu --enable-debug --enable-java-gc=boehm
--enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.3 20040110 (prerelease) (Debian)


I searched the web about this issue and found other people that asked about this
issue on different mailing lists, but no one seems to have a solution or a work
around.

By digging in the g77 doc I found the ALWAYS_FLUSH dissertation, but it seems
(at least to me) that this macro is no longer defined in libg2c, just to
*increase* NFS I/O performance. So, I'm a bit puzzled...


How to reproduce the strange behaviour:

The following is done on a RedHat Enterprise Linux 3.0 machine having other
RHEL3 filesystems mounted via NFS.

Let's start on the local filesystem:

$ df --si .
Filesystem             Size   Used  Avail Use% Mounted on
/dev/cciss/c0d0p2     139GB  8.1GB  124GB   7% /
$ ls
mywrite.f
$ cat mywrite.f 
      program mywrite

c     constant definitions
c     """"""""""""""""""""
      integer n
      parameter (n=800000)

c     variable declarations
c     """""""""""""""""""""
      integer i
      complex cvar

c     write out unformatted file
c     """"""""""""""""""""""""""
      open (unit=3,file='myout.dat',form='unformatted')
      close(unit=3,status='delete')
      open (unit=3,file='myout.dat',form='unformatted')
      rewind 3

      cvar = (1.23e20,0.31e20)

      write (3) n
      do 10 i = 1, n
        cvar = cvar/1.1
        write (3) cvar
 10   continue

      close (unit=3)

      stop
      end
$ g77 -static -o mywrite mywrite.f 
$ \time -o localtime ./mywrite
$ cat localtime 
3.52user 12.06system 0:15.88elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (33major+16minor)pagefaults 0swaps


Now let's turn to the remote, NFS-mounted filesystem:

$ df --si .
Filesystem             Size   Used  Avail Use% Mounted on
192.168.0.10:/home10b
                       79GB  199MB   75GB   1% /home10b
$ cat /proc/mounts | grep 10b
192.168.0.10:/home10b /home10b nfs rw,v3,rsize=8192,wsize=8192,hard,udp,lock,add
r=192.168.0.10 0 0
$ ls 
mywrite.f
$ g77 -static -o mywrite mywrite.f 
$ \time -o nfstime ./mywrite


Well, after about *one hour*, it's still running: the output file is about *one
half* of its final size and still (slowly) growing...   :-(
I'll add the result when it's finished...


Any ideas?
Why do I obtain unreasonable times (two hours for a 13 Mbyte output file that
can be copied to the same NFS-mounted filesystem in less than one half of a
second with cp)?
Any help will be much appreciated.

TNX

-- 
           Summary: long write times via NFS
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: e-frx at arnone dot de dot unifi dot it
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-pc-linux-gnu
  GCC host triplet: i386-pc-linux-gnu
GCC target triplet: i386-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16970