Issue with grep -i (on i386 only?)

[Alex Burke]

On Wednesday, November 4, 2009, Eygene Ryabinkin <rea-fbsd at codelabs.ru> wrote:
> Mel, good day.
>
> Tue, Nov 03, 2009 at 09:22:28PM +0100, Mel Flynn wrote:
>> So on the laptop I modified the testscript as it is attached now and
>> while there is still a significant delay, the wallclock time is less
>> then half, when the expression is rewritten with the same meaning:
>> =>>> 16777216
>>     =>>> fgrep
>>         0.04 real         0.03 user         0.00 sys
>>         0.05 real         0.03 user         0.01 sys
>>         0.02 real         0.00 user         0.00 sys
>>     =>>> pcregrep
>>         0.26 real         0.21 user         0.02 sys
>>         0.26 real         0.22 user         0.02 sys
>>         0.44 real         0.35 user         0.01 sys
>>     =>>> grep
>>         0.04 real         0.04 user         0.00 sys
>>         4.45 real         4.15 user         0.01 sys
>>         2.00 real         1.81 user         0.00 sys <-- [fF][Oo][Oo]
>
> Just did a quick test on the 8.0-RC2/i386 with very old Athlon processor:
> -----
> =>>> 16777216
>     =>>> fgrep
>         0,09 real         0,04 user         0,05 sys
>         0,18 real         0,06 user         0,03 sys
>         0,05 real         0,01 user         0,04 sys
>     =>>> pcregrep
>         0,47 real         0,29 user         0,07 sys
>         0,52 real         0,33 user         0,07 sys
>         0,77 real         0,45 user         0,03 sys
>     =>>> grep
>         0,09 real         0,08 user         0,01 sys
>         0,10 real         0,04 user         0,05 sys
>         0,23 real         0,12 user         0,03 sys
> -----
> Pattern for the plain 'grep' is stable: first and second variants always
> give the same time within a 0.01 second variation and the last variant
> gives 2x slowdown.
>
> I tried sizes up to the 64M -- the pattern stays.  The same stuff for
> the amd64, so in my case I don't see the difference in behaviour.  So,
> maybe, the problem isn't 32 vs 64 but lies somewhere else.
>
>> attached a little test script for grep's -i performance.
>
> Some notes about the script, especially if (or some variant of it)
> will be included to the testing framework.
>
>> #!/bin/sh
>> # vim: ts=4 sw=4 noet tw=78 ai
>>
>> PCREGREP=`which pcregrep`
>> BSDGREP=`which bsdgrep`
>> [ -n ${PCREGREP} ] && PCREGREP=`basename ${PCREGREP}`
>> [ -n ${BSDGREP} ] && BSDGREP=`basename ${BSDGREP}`
>
> You'll want '[ -n "${PCREGREP}" ] && ...' (with quoted variable) to
> really achieve the kind of test you wanted.
>
>> if [ ! -x /usr/bin/jot ]; then
>>       echo "Need jot"
>>       exit 1
>> fi
>> if [ ! -x /usr/bin/rs ]; then
>>       echo "Need rs"
>>       exit 1
>> fi
>
> Probably this is better be written as
> -----
> for prog in jot rs; do
>         if [ -z "`which "$prog"`" ]; then
>                 echo "Need $prog"
>                 exit 1
>         fi
> done
> -----
> because the latter code uses unqualified 'jot' and 'rs'.
>
>> for b in ${BYTES}; do
>>       TMPFILE=`mktemp -t ${me}`
>>       if [ ! -f ${TMPFILE} ]; then
>>               echo Can\'t create tmp files in ${TMPDIR:="/tmp"}
>>               exit 2
>>       fi
>>       jot -r -c ${b} a z |rs -g 0 20 > ${TMPFILE}
>>       echo "=>>> ${b}"
>>       for prog in fgrep ${PCREGREP} ${BSDGREP} grep ; do
>>               echo "    =>>> ${prog}"
>>               /usr/bin/time ${prog} foo ${TMPFILE} >/dev/null
>>               /usr/bin/time ${prog} -i foo ${TMPFILE} >/dev/null
>>               /usr/bin/time ${prog} '[fF][Oo][Oo]' ${TMPFILE} >/dev/null
>>       done
>>       rm ${TMPFILE}
>> done
>
> Most likely, it is better to create the temporary file only once
> and to trap the signals with the file removal -- this will handle
> the cases when user presses ^C during the execution -- temporary
> file should be cleaned in this case.  The code is simple:
> -----
> TMPFILE=`mktemp -t ${me}`
> if [ ! -f ${TMPFILE} ]; then
>         echo "Can't create tmp file in ${TMPDIR:=/tmp}"
>         exit 2
> fi
> trap 'rm -f "${TMPFILE}"' 0 1 2 3 15
> -----
>
> Attaching modified version with the bonus -- 'K' and 'M' size prefixes:
> it was boring to specify many digits when I had played with sizes ;))
> --
> Eygene
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>