On Friday, March 30, 2012 04:56:17 PM Jeshua Lacock did opine:
> On Mar 30, 2012, at 1:20 AM, Viesturs Lؤپcis wrote:
> >> Does anyone know of some known settings to try disabling in CMOS to
> >> possibly get lower numbers? My 1.0ms Max Jitter is under 9300, but
> >> if possible I would like to get it even lower.
> >
> > IMHO it is very good number already. You have max jitter of 9,3 us in
> > a 1000 us thread, so the max deviance is less than 1%, LinuxCNC will
> > perfectly handle that.
> > At the moment I can remember of 2 things to do, if You want to try:
> > 1) for Intel processors, hyperthreading might be disabled;
> > 2) for multi-core processors, one or more processors can be isolated
> > exclusively for real-time tasks with isolcpus parameter;
> >
> > http://wiki.linuxcnc.org/cgi-bin/wiki.pl?RealTime
>
> Thanks for your explanation Viesturs!
>
> And, that is very interesting! When I run the CPU hog, my max jitter
> goes down to about 1,000!
>
> I would like to set the CPU as instructed, but I have never used grub
> before. I assume I add "isolcpus=1" to the /boot/grub/grub.cfg file -
> but I am not sure where to add it. Any suggestions would be greatly
> appreciated, thanks!
>
>
> Best,
>
> Jeshua Lacock
> Founder/Engineer
> 3DTOPO Incorporated
> <http://3DTOPO.com>
> Phone: 208.462.4171
It is better to put it as a file in /etc/grub.d/, named
as "07_rtai" as this way it can maybe survive a kernel update.
NOTE: My mailers word wrap has been turned off, so should
yours to properly read this.
The file:+++++ (clip below) +++++
#! /bin/sh -e
# grub-mkconfig helper script.
# Copyright (C) 2006,2007,2008,2009,2010 Free Software Foundation, Inc.
#
# GRUB 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.
#
# GRUB 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 GRUB. If not, see <http://www.gnu.org/licenses/>.
##############################################################################
# this is Kent Reed's attempt to create 07_rtai from 10_linux 2011/04/07
# V0.1
#
# produces grub2 boot menu entries for rtai kernels appending "isolcpus=1"
# after $GRUB_CMDLINE_LINUX_DEFAULT (whose value is set in /etc/default/grub)
# NOTE1: an unmodified 10_linux will later create more grub entries for the
# same kernels using only $GRUB_CMDLINE_LINUX_DEFAULT
# NOTE2: deep in grub2 is a list of allowable user-defined keys so
# I couldn't simply define a new GRUB_CMDLINE_RTAI_DEFAULT
# in /etc/default/grub---SIGH!
# NOTE3: following this comment block, changes to 10_linux are preceded
# by lines beginning #KAR:
# NOTE4: since grub scripts aren't true shell scripts, I made no attempt
# to break new ground. I just copied and modified existing code
# NOTE5: does it make sense to add isolcpus=1 to recovery mode?
##############################################################################
prefix=/usr
exec_prefix=${prefix}
bindir=${exec_prefix}/bin
libdir=${exec_prefix}/lib
. ${libdir}/grub/grub-mkconfig_lib
#KAR: define new local strings for convenience
# if you want to change the rtai-kernel boot parameters, here's an easy
# place to do it.
ISOLCPUS="isolcpus=1"
GRUB_CMDLINE_LINUX_RTAI="${GRUB_CMDLINE_LINUX_DEFAULT} ${ISOLCPUS}"
export TEXTDOMAIN=grub
export TEXTDOMAINDIR=@LOCALEDIR@
CLASS="--class gnu-linux --class gnu --class os"
if [ "x${GRUB_DISTRIBUTOR}" = "x" ] ; then
OS=GNU/Linux
else
OS="${GRUB_DISTRIBUTOR}"
CLASS="--class $(echo ${GRUB_DISTRIBUTOR} | tr '[A-Z]' '[a-z]' | cut -d' ' -f1) ${CLASS}"
fi
# loop-AES arranges things so that /dev/loop/X can be our root device, but
# the initrds that Linux uses don't like that.
case ${GRUB_DEVICE} in
/dev/loop/*|/dev/loop[0-9])
GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
# We can't cope with devices loop-mounted from files here.
case ${GRUB_DEVICE} in
/dev/*) ;;
*) exit 0 ;;
esac
;;
esac
if [ "x${GRUB_DEVICE_UUID}" = "x" ] || [ "x${GRUB_DISABLE_LINUX_UUID}" = "xtrue" ] \
|| ! test -e "/dev/disk/by-uuid/${GRUB_DEVICE_UUID}" \
|| [ "`grub-probe -t abstraction --device ${GRUB_DEVICE} | sed -e 's,.*\(lvm\).*,\1,'`" = "lvm" ] ; then
LINUX_ROOT_DEVICE=${GRUB_DEVICE}
else
LINUX_ROOT_DEVICE=UUID=${GRUB_DEVICE_UUID}
fi
# add crashkernel option if we have the required tools
if [ -x "/usr/bin/makedumpfile" ] && [ -x "/sbin/kexec" ]; then
GRUB_CMDLINE_EXTRA="$GRUB_CMDLINE_EXTRA crashkernel=384M-2G:64M,2G-:128M"
fi
linux_entry ()
{
os="$1"
version="$2"
recovery="$3"
args="$4"
if ${recovery} ; then
title="$(gettext_quoted "%s, with Linux %s (recovery mode)")"
else
#KAR: augment title to make sensible grub2 boot menu entry
title="$(gettext_quoted "%s, with Linux %s (${ISOLCPUS})")"
fi
printf "menuentry '${title}' ${CLASS} {\n" "${os}" "${version}"
cat << EOF
recordfail
EOF
save_default_entry | sed -e "s/^/\t/"
if [ "x$GRUB_GFXPAYLOAD_LINUX" != x ]; then
cat << EOF
set gfxpayload=$GRUB_GFXPAYLOAD_LINUX
EOF
fi
if [ -z "${prepare_boot_cache}" ]; then
prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"
fi
printf '%s\n' "${prepare_boot_cache}"
if [ "x$5" != "xquiet" ]; then
cat << EOF
echo '$(printf "$(gettext_quoted "Loading Linux %s ...")" ${version})'
EOF
fi
cat << EOF
linux ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args}
EOF
if [ "x$5" != "xquiet" ]; then
cat << EOF
echo '$(gettext_quoted "Loading initial ramdisk ...")'
EOF
fi
if test -n "${initrd}" ; then
cat << EOF
initrd ${rel_dirname}/${initrd}
EOF
fi
cat << EOF
}
EOF
}
blacklisted_kernel() {
local r=""
case "${1}" in
*-ec2) r="linux-ec2";; # LP: #671097
esac
[ -n "${r}" ] && { echo "Skipping linux image [$r]: ${1}" >&2; return 0; }
return 1;
}
#KAR: add new function to test if kernel name ends in -rtai
rtai_kernel() {
local r=""
case "${1}" in
*-rtai) r="true";;
esac
[ -n "${r}" ] && { return 0; }
return 1;
}
#KAR: add rtai-kernel test in determination of suitable kernels
list=`for i in /boot/vmlinu[xz]-* /vmlinu[xz]-* ; do
if grub_file_is_not_garbage "$i" &&
! blacklisted_kernel "$i" &&
rtai_kernel "$i" ; then
echo -n "$i ";
fi
done`
prepare_boot_cache=
while [ "x$list" != "x" ] ; do
linux=`version_find_latest $list`
#KAR: modify message
echo "Found rtai linux image: $linux" >&2
basename=`basename $linux`
dirname=`dirname $linux`
rel_dirname=`make_system_path_relative_to_its_root $dirname`
version=`echo $basename | sed -e "s,^[^0-9]*-,,g"`
alt_version=`echo $version | sed -e "s,\.old$,,g"`
linux_root_device_thisversion="${LINUX_ROOT_DEVICE}"
initrd=
for i in "initrd.img-${version}" "initrd-${version}.img" \
"initrd-${version}" "initrd.img-${alt_version}" \
"initrd-${alt_version}.img" "initrd-${alt_version}"; do
if test -e "${dirname}/${i}" ; then
initrd="$i"
break
fi
done
if test -n "${initrd}" ; then
#KAR: modify message
echo "Found rtai initrd image: ${dirname}/${initrd}" >&2
else
# "UUID=" magic is parsed by initrds. Since there's no initrd, it can't work here.
linux_root_device_thisversion=${GRUB_DEVICE}
fi
#KAR: change original production to use GRUB_CMDLINE_LINUX_RTAI instead of GRUB_CMDLINE_LINUX_DEFAULT
linux_entry "${OS}" "${version}" false \
"${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_EXTRA} ${GRUB_CMDLINE_LINUX_RTAI}" \
quiet
if [ "x${GRUB_DISABLE_LINUX_RECOVERY}" != "xtrue" ]; then
linux_entry "${OS}" "${version}" true \
"single ${GRUB_CMDLINE_LINUX}"
fi
list=`echo $list | tr ' ' '\n' | grep -vx $linux | tr '\n' ' '`
done
==============clip above & fix mailer damages if any========
I _think_ this is in the wiki someplace too.
Many thanks to Kent Reed for this bit of magic.
Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene>
The rule on staying alive as a forecaster is to give 'em a number or
give 'em a date, but never give 'em both at once.
-- Jane Bryant Quinn
|