79 lines
3.1 KiB
C
79 lines
3.1 KiB
C
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/* I/O block size definitions for coreutils
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Copyright (C) 1989-2020 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Include this file _after_ system headers if possible. */
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/* sys/stat.h will already have been included by system.h. */
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#include "stat-size.h"
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/* As of May 2014, 128KiB is determined to be the minimium
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blksize to best minimize system call overhead.
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This can be tested with this script:
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for i in $(seq 0 10); do
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bs=$((1024*2**$i))
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printf "%7s=" $bs
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timeout --foreground -sINT 2 \
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dd bs=$bs if=/dev/zero of=/dev/null 2>&1 \
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| sed -n 's/.* \([0-9.]* [GM]B\/s\)/\1/p'
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done
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With the results shown for these systems:
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system #1: 1.7GHz pentium-m with 400MHz DDR2 RAM, arch=i686
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system #2: 2.1GHz i3-2310M with 1333MHz DDR3 RAM, arch=x86_64
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system #3: 3.2GHz i7-970 with 1333MHz DDR3, arch=x86_64
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system #4: 2.20GHz Xeon E5-2660 with 1333MHz DDR3, arch=x86_64
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system #5: 2.30GHz i7-3615QM with 1600MHz DDR3, arch=x86_64
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system #6: 1.30GHz i5-4250U with 1-channel 1600MHz DDR3, arch=x86_64
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system #7: 3.55GHz IBM,8231-E2B with 1066MHz DDR3, POWER7 revision 2.1
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per-system transfer rate (GB/s)
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blksize #1 #2 #3 #4 #5 #6 #7
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------------------------------------------------------------------------
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1024 .73 1.7 2.6 .64 1.0 2.5 1.3
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2048 1.3 3.0 4.4 1.2 2.0 4.4 2.5
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4096 2.4 5.1 6.5 2.3 3.7 7.4 4.8
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8192 3.5 7.3 8.5 4.0 6.0 10.4 9.2
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16384 3.9 9.4 10.1 6.3 8.3 13.3 16.8
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32768 5.2 9.9 11.1 8.1 10.7 13.2 28.0
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65536 5.3 11.2 12.0 10.6 12.8 16.1 41.4
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131072 5.5 11.8 12.3 12.1 14.0 16.7 54.8
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262144 5.7 11.6 12.5 12.3 14.7 16.4 40.0
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524288 5.7 11.4 12.5 12.1 14.7 15.5 34.5
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1048576 5.8 11.4 12.6 12.2 14.9 15.7 36.5
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Note that this is to minimize system call overhead.
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Other values may be appropriate to minimize file system
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or disk overhead. For example on my current GNU/Linux system
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the readahead setting is 128KiB which was read using:
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file="."
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device=$(df --output=source --local "$file" | tail -n1)
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echo $(( $(blockdev --getra $device) * 512 ))
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However there isn't a portable way to get the above.
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In the future we could use the above method if available
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and default to io_blksize() if not.
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*/
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enum { IO_BUFSIZE = 128*1024 };
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static inline size_t
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io_blksize (struct stat sb)
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{
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return MAX (IO_BUFSIZE, ST_BLKSIZE (sb));
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}
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