[Patch, gfortran]: PR21820, 23363 etc.: chuck mmap

[Janne Blomqvist <jblomqvi at cc dot hut dot fi>]

Hello,

the attached patch provides a partial fix for the performance issues
in PR 21820 and 23363. Partial, as in improving performance 20-fold
for some cases but still being far away from other compilers.  The
patch also solves all mmap related correctness problems, by removing
mmap support from the runtime library.

I gave some reason why I think mmap is not needed here:

http://gcc.gnu.org/ml/fortran/2005-08/msg00017.html

Some analysis on why gfortran I/O is slow at

http://gcc.gnu.org/ml/fortran/2005-06/msg00084.html

Timing measurements on Linux-x86 for this patch:

PR 21820

No mmap:

./pr21820.gfortran_no_mmap  0,02s user 0,00s system 82% cpu 0,024 total

mmap (current HEAD):

./pr21820.gfortran  0,16s user 0,40s system 102% cpu 0,547 total

delete file before executing for HEAD:

./pr21820.gfortran  0,02s user 0,01s system 134% cpu 0,022 total

ifort 8.0:

./pr21820.ifort  0,01s user 0,00s system 324% cpu 0,003 total



PR 23363

no mmap:

./rdiska.gfortran_no_mmap  0,75s user 0,01s system 98% cpu 0,774 total

with mmap (HEAD):

./rdiska.gfortran  4,11s user 9,38s system 99% cpu 13,560 total

delete file before running HEAD:

./rdiska.gfortran  0,94s user 0,03s system 97% cpu 0,990 total

g77:

./rdiska.g77  0,00s user 0,02s system 74% cpu 0,027 total

ifort 8.0:

./rdiska.ifort  0,03s user 0,11s system 102% cpu 0,137 total


Changelog and patch attached.


-- 
Janne Blomqvist

Attachment: ChangeLog
Description: Text document

Attachment: chuck_mmap.patch
Description: Text document