diff options
Diffstat (limited to 'src')
-rw-r--r-- | src/system.h | 90 |
1 files changed, 45 insertions, 45 deletions
diff --git a/src/system.h b/src/system.h index dbb4da1ed..eafcc2523 100644 --- a/src/system.h +++ b/src/system.h @@ -221,51 +221,6 @@ 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 @@ -701,4 +656,49 @@ bad_cast (char const *s) return (char *) s; } +/* 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)); +} + void usage (int status) ATTRIBUTE_NORETURN; |