Matthew Dillon 1b7e3dafdf Fix a file-rewrite performance case for UFS[2]. When rewriting portions ... of a file in chunks that are less then the filesystem block size, if the data is not already cached the system will perform a read-before-write. The problem is that it does this on a block-by-block basis, breaking up the I/Os and making clustering impossible for the writes. Programs such as INN using cyclic file buffers suffer greatly. This problem is only going to get worse as we use larger and larger filesystem block sizes. The solution is to extend the sequential heuristic so UFS[2] can perform a far larger read and readahead when dealing with this case. (note: maximum disk write bandwidth is 27MB/sec thru filesystem) (note: filesystem blocksize in test is 8K (1K frag)) dd if=/dev/zero of=test.dat bs=1k count=2m conv=notrunc Before: (note half of these are reads) tty da0 da1 acd0 cpu tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id 0 76 14.21 598 8.30 0.00 0 0.00 0.00 0 0.00 0 0 7 1 92 0 76 14.09 813 11.19 0.00 0 0.00 0.00 0 0.00 0 0 9 5 86 0 76 14.28 821 11.45 0.00 0 0.00 0.00 0 0.00 0 0 8 1 91 After: (note half of these are reads) tty da0 da1 acd0 cpu tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id 0 76 63.62 434 26.99 0.00 0 0.00 0.00 0 0.00 0 0 18 1 80 0 76 63.58 424 26.30 0.00 0 0.00 0.00 0 0.00 0 0 17 2 82 0 76 63.82 438 27.32 0.00 0 0.00 0.00 0 0.00 1 0 19 2 79 Reviewed by: mckusick Approved by: re X-MFC after: immediately (was heavily tested in -stable for 4 months)		2002-10-18 22:52:41 +00:00
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ffs	Fix a file-rewrite performance case for UFS[2]. When rewriting portions	2002-10-18 22:52:41 +00:00
ufs	Fix a file-rewrite performance case for UFS[2]. When rewriting portions	2002-10-18 22:52:41 +00:00