Hi Harald, Yes i tried other values.
It seems that the value set in the foreseen environment variable is just ignored. And always a buffer size of 8kiB is used, which is the default values for formatted I/O harcoded in libgfortran. The only way to change this value is editing and recompiling the libgfortran. Best. Denis ________________________________ From: Harald Anlauf <anl...@gmx.de> Sent: Friday, February 25, 2022 9:44:53 PM To: Bertini, Denis Dr. Cc: Tobias Burnus; fortran@gcc.gnu.org Subject: Re: Problem setting buffer size for gfortran ( v 11.2) Hi Denis, > export GFORTRAN_UNFORMATTED_BUFFER_SIZE=10000 > export GFORTRAN_FORMATTED_BUFFER_SIZE=10000 > export GFORTRAN_UNBUFFERED_ALL=n > > From the output log indeed i got the correct env. variable as i set: > > > GFORTRAN_FORMATTED_BUFFER_SIZE=10000 > > > But from strace output i got always > > >>>>>>>>>>>>>>>>>>>>>>> > > write(3, > "\0\0\0\0\0\0\10@\0\0\0\340\314\314\10@\0\0\0\240\231\231\t@\0\0\0`ff\n@"..., > 8192) = 8192 > write(3, > "\0\0\0@33\v@\0\0\0\0\0\0\f@\0\0\0\340\314\314\f@\0\0\0\240\231\231\r@"..., > 8192) = 8192 > write(3, "\0\0\0`ff\16@\0\0\0@33\17@\0\0\0\0\0\0\20@\0\0\0`ff\20@"..., 8192) > = 8192 > write(3, > "\0\0\0\340\314\314\20@\0\0\0@33\21@\0\0\0\240\231\231\21@\0\0\0\0\0\0\22@"..., > 8192) = 8192 > write(3, > "\0\0\0`ff\22@\0\0\0\340\314\314\22@\0\0\0@33\23@\0\0\0\240\231\231\23@"..., > 8192) = 8192 > write(3, > "\0\0\0\0\0\0\24@\0\0\0`ff\24@\0\0\0\340\314\314\24@\0\0\0@33\25@"..., 8192) > = 8192 > ..... >>>>>>>>>>>>>>>>>>> > Showing the fixed that still a 8kiB buffer size is effectively ude in I/O... did you ever think of trying other values than 10000? On my Linux laptop, buffering is done in multiples of 2k. If I set GFORTRAN_UNFORMATTED_BUFFER_SIZE=14000, I get writes in sizes of 12288. Which is likely more efficient than asking for exactly 14000. Cheers, Harald
