https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91030
--- Comment #39 from Janne Blomqvist <jb at gcc dot gnu.org> --- Now, with the fixed benchmark in the previous comment, on Lustre (version 2.5) system I get: Test using 250000000 bytes Block size of file system: 4096 bs = 1024, 53.27 MiB/s bs = 2048, 73.99 MiB/s bs = 4096, 222.41 MiB/s bs = 8192, 351.38 MiB/s bs = 16384, 483.86 MiB/s bs = 32768, 583.76 MiB/s bs = 65536, 677.11 MiB/s bs = 131072, 748.60 MiB/s bs = 262144, 700.69 MiB/s bs = 524288, 811.76 MiB/s bs = 1048576, 1032.99 MiB/s bs = 2097152, 1034.03 MiB/s bs = 4194304, 1063.74 MiB/s bs = 8388608, 1030.15 MiB/s bs = 16777216, 1084.82 MiB/s bs = 33554432, 1067.05 MiB/s bs = 67108864, 1063.79 MiB/s On the same system, on a NFS filesystem connected with Infiniband I get: Test using 250000000 bytes Block size of file system: 1048576 bs = 1024, 301.41 MiB/s bs = 2048, 351.51 MiB/s bs = 4096, 471.39 MiB/s bs = 8192, 444.61 MiB/s bs = 16384, 510.88 MiB/s bs = 32768, 527.99 MiB/s bs = 65536, 516.57 MiB/s bs = 131072, 481.38 MiB/s bs = 262144, 514.29 MiB/s bs = 524288, 462.06 MiB/s bs = 1048576, 528.30 MiB/s bs = 2097152, 526.76 MiB/s bs = 4194304, 501.09 MiB/s bs = 8388608, 493.61 MiB/s bs = 16777216, 550.24 MiB/s bs = 33554432, 532.20 MiB/s bs = 67108864, 532.82 MiB/s So for Lustre, a buffer size bigger than the current 8 kB at least seems justified. While Lustre sees improvements all the way to 1 MB buffer size, such large buffers by default seems a bit excessive.
