On Mon, 8 Jul 2019 09:05:04 -0700 Steve Kargl <s...@troutmask.apl.washington.edu> wrote:
> On Mon, Jul 08, 2019 at 04:02:17PM +0300, Janne Blomqvist wrote: > > > > 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.) GFORTRAN_BUFFER_SIZE_FORMATTED sounds a bit odd, maybe GFORTRAN_(UN)FORMATTED_BUFFER_SIZE would read more natural. And let me note 2 flaws in the benchmark: > left = N; > w = p; > t1 = walltime(); > while (left > 0) > { > if (left >= blocksize) > to_write = blocksize; > else > to_write = left; > > write (fd, w, blocksize); 1) this should write to_write, not blocksize i assume. 2) you don't catch short writes > w += to_write; > left -= to_write; > } So, short of using iozone, it should probably be more like (modulo typos): left = N; w = p; t1 = walltime(); while (left > 0) { if (left >= blocksize) to_write = blocksize; else to_write = left; while (to_write > 0) { errno = 0; ssize_t wrote = write (fd, w, to_write); if (wrote < 0 && errno != EINTR) /* retry EINTR or bail */ break; w += wrote; left -= wrote; to_write -= wrote; } } thanks,
