diff options
Diffstat (limited to 'src/system.h')
| -rw-r--r-- | src/system.h | 50 |
1 files changed, 48 insertions, 2 deletions
diff --git a/src/system.h b/src/system.h index ba74da448..dbb4da1ed 100644 --- a/src/system.h +++ b/src/system.h @@ -147,6 +147,9 @@ enum # define D_INO(dp) NOT_AN_INODE_NUMBER #endif +/* include here for SIZE_MAX. */ +#include <inttypes.h> + /* Get or fake the disk device blocksize. Usually defined by sys/param.h (if at all). */ #if !defined DEV_BSIZE && defined BSIZE @@ -218,6 +221,51 @@ enum # endif #endif +/* 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 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)); +} + /* Redirection and wildcarding when done by the utility itself. Generally a noop, but used in particular for native VMS. */ #ifndef initialize_main @@ -228,8 +276,6 @@ enum #include "timespec.h" -#include <inttypes.h> - #include <ctype.h> #if ! (defined isblank || HAVE_DECL_ISBLANK) |