1 files changed, 66 insertions, 0 deletions
diff --git a/src/ioblksize.h b/src/ioblksize.h
new file mode 100644
index 000000000..eaeced30b
--- /dev/null
+++ b/src/ioblksize.h
@@ -0,0 +1,66 @@
+/* I/O block size definitions for coreutils
+   Copyright (C) 1989, 1991-2011 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Include this file _after_ system headers if possible.  */
+
+/* sys/stat.h will already have been included by system.h. */
+#include "stat-size.h"
+
+
+/* As of Mar 2009, 32KiB is determined to be the minimium
+   blksize to best minimize system call overhead.
+   This can be tested with this script with the results
+   shown for a 1.7GHz pentium-m with 2GB of 400MHz DDR2 RAM:
+
+   for i in $(seq 0 10); do
+     size=$((8*1024**3)) #ensure this is big enough
+     bs=$((1024*2**$i))
+     printf "%7s=" $bs
+     dd bs=$bs if=/dev/zero of=/dev/null count=$(($size/$bs)) 2>&1 |
+     sed -n 's/.* \([0-9.]* [GM]B\/s\)/\1/p'
+   done
+
+      1024=734 MB/s
+      2048=1.3 GB/s
+      4096=2.4 GB/s
+      8192=3.5 GB/s
+     16384=3.9 GB/s
+     32768=5.2 GB/s
+     65536=5.3 GB/s
+    131072=5.5 GB/s
+    262144=5.7 GB/s
+    524288=5.7 GB/s
+   1048576=5.8 GB/s
+
+   Note that this is to minimize system call overhead.
+   Other values may be appropriate to minimize file system
+   or disk overhead.  For example on my current GNU/Linux system
+   the readahead setting is 128KiB which was read using:
+
+   file="."
+   device=$(df -P --local "$file" | tail -n1 | cut -d' ' -f1)
+   echo $(( $(blockdev --getra $device) * 512 ))
+
+   However there isn't a portable way to get the above.
+   In the future we could use the above method if available
+   and default to io_blksize() if not.
+ */
+enum { IO_BUFSIZE = 32*1024 };
+static inline size_t
+io_blksize (struct stat sb)
+{
+  return MAX (IO_BUFSIZE, ST_BLKSIZE (sb));
+}