On Mon, Jul 8, 2019 at 11:18 AM Manfred Schwarb <manfre...@gmx.ch> wrote: > > Am 07.07.19 um 22:13 schrieb Thomas Koenig: > > Hello world, > > > > the attached patch sets the I/O block size for unformatted files to > > 2**17 and makes this, and the block size for formatted files, > > adjustable via environment variables. > > > > The main reason is that -fconvert=big-endian was quite slow on > > some HPC systems. A bigger buffer should eliminate that. Also, > > People who use unformatted files are likely to write large amounts > > of data, so this seems like a good fit. Finally, some benchmarking > > showed that 131072 seemed like a good value to use. Thanks to Jerry > > for support. > > > > I didn't change the value for formatted files because, frankly, we are > > using a lot of CPU for converting numbers there, so any gain > > negligible (unless somebody comes up with a benchmark which says > > otherwise). > > formatted write: Did you try writing to an USB stick or similar? I guess > for flash based devices anything below 64k will slow down operation. > Computers like Raspberry Pi and the like often have flash based storage, > and it is not extremely unrealistic to run fortran programs on them.
Good point. If you happen to have a USB stick handy, can you try the simple C benchmark program at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91030#c38 ? (the kernel will coalesce IO's by itself, so the granularity of IO syscalls is not necessarily the same as the actual IO to devices. Network filesystems like NFS/Lustre/GPFS may have less latitude here due to coherency requirements etc.) -- Janne Blomqvist
