[Bug libfortran/33985] access="stream",form="unformatted" doesn't buffer

["jvdelisle at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #14 from jvdelisle at gcc dot gnu dot org  2007-12-01 04:22 -------
This is embarrassing and good at the same time:

Index: unix.c
===================================================================
--- unix.c      (revision 130547)
+++ unix.c      (working copy)

@@ -669,11 +669,8 @@ fd_seek (unix_stream * s, gfc_offset off
   if (s->file_length == -1)
     return SUCCESS;

-  if (s->physical_offset == offset) /* Are we lucky and avoid syscall?  */
-    {
-      s->logical_offset = offset;
-      return SUCCESS;
-    }
+  if (s->logical_offset == offset) /* Are we lucky and avoid syscall?  */
+    return SUCCESS;

   if (lseek (s->fd, offset, SEEK_SET) >= 0)
     {

According to the comment we have been unlucky for a long time.  :) With this
simple change alone, my sequential read benchmark goes from 23 seconds to .5
seconds.  There is a regression in backspace_6.f90 which implies we need to fix
back space and leave the above fix in place if possible.  The read test I am
using is reading a 36 megabyte unformatted file with ACCESS="stream".  This is
impressive!

My write test with same file goes from about 6 seconds to about .5 seconds as
well.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33985