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Subject: | Re: Run a Cygwin process with "higher" scheduler priority |
To: | cygwin AT cygwin DOT com |
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Message-ID: | <eb337eaf-40d4-5113-0629-43fcb76a8ffc@t-online.de> |
Date: | Sun, 15 Oct 2023 15:04:06 +0200 |
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From: | Christian Franke via Cygwin <cygwin AT cygwin DOT com> |
Reply-To: | Christian Franke <Christian DOT Franke AT t-online DOT de> |
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Brian Inglis via Cygwin wrote: > On 2023-10-14 07:47, Eliot Moss via Cygwin wrote: >> On 10/14/2023 7:39 AM, Cedric Blancher via Cygwin wrote: >>> On Fri, 11 Aug 2023 at 19:14, Brian Inglis wrote: >>>> ... >>> >>>> ... >>>> $ cygcheck -p usr/bin/chrt >>>> Found 2 matches for usr/bin/chrt >>>> util-linux-debuginfo-2.33.1-2 - util-linux-debuginfo: Debug info >>>> for util-linux >>>> util-linux-2.33.1-2 - util-linux: Collection of basic system utilities >>>> $ cygcheck -p usr/bin/taskset >>>> Found 2 matches for usr/bin/taskset >>>> util-linux-debuginfo-2.33.1-2 - util-linux-debuginfo: Debug info >>>> for util-linux >>>> util-linux-2.33.1-2 - util-linux: Collection of basic system utilities >>>> so you may need to install util-linux (coreutils is already >>>> installed as a base >>>> package for Cygwin) then: >>>>         $ man nice renice taskset chrt >>> chrt does not work, the syscalls for realtime seem to be not >>> implemented. These are partly implemented, but sched_setscheduler() always fails with ENOSYS because scheduler policy (SCHED_*) cannot be changed on Windows. Changing priority only with sched_setparam() would work, but this is not used by chrt. >>>> You may need to run these from an elevated admin shell for other >>>> user ids, >>>> unowned processes, or higher (negative) priority. >>>> It has been years since I tried these so can no longer remember if -20 >>>> corresponds to Windows "RealTime" or if you need to use PowerShell >>>> to set that e.g. >>>>         $proc  = Get-Process -ProcessName "..." >>>>         $proc.PriorityClass    = "RealTime" >>>> and that needs to be done from an elevated admin (Power)Shell. >>>> Of course, never set that on any system except on a very idle, very >>>> I/O bound, >>>> well tested process, such as ntpd, that needs stably fast interrupt >>>> service and >>>> non-preemptible cpu access for ms every few seconds, preferably on >>>> a single or >>>> few cpus to which affinity is set. >>> Is there anything in /proc which can tell me the current *Windows* >>> scheduler priority level? Or a command line tool? >> I recall getting taskset going in util-linux a while back, but I don't >> recall working on priority related things. You could look into the >> cygwin source code to see how Windows priorities relate to the priority >> values in Cygwin. Then you may be able just to use /proc/[pid]/stat >> read out what you want. > > ISTR testing nice/renice, and found it was a simple priority mapping > to/from Unix to Windows Idle to RealTime (at the time, process > Affinity was not supported, so went with a PowerShell startup script > instead); see: > > https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/sched.cc#l107 > > > https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/sched.cc#l234 > > > https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/sched.cc#l277 > The above maps priorities for sched_*() API. The mapping for nice() and get/setpriority() is done here: https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/miscfuncs.cc;h=767384f#l110 > They are documented in proc(5) /proc/PID/stat fields 18 priority and > 19 nice typically 20 and 0, as shown by `top` PR and NI, shown by > `procps -l` as 80 and 0, and not shown by Cygwin `ps`. On Cygwin, field 18 is always equal to (field_19 + 20). The priority value returned by sched_getparam() is different and could be shown with 'chrt -p PID'. The output from the command 'nice' without parameter may differ from /proc/PID/stat field 19 because the latter always reinterprets the current Windows prio class. This script prints a table of 'nice' outputs, /proc/PID/stat fields 19 and 18, result of sched_getparam() and corresponding Windows prio class for different 'nice -n ...' commands: #!/bin/bash echo "COMMAND   : NICE STAT STPRI RTPRI WINPRI" for i in {-21..20}; do  nice -n $i sh -e -c '    n=$(nice)    s=$(cut -d" " -f19 /proc/$$/stat)    p=$(cut -d" " -f18 /proc/$$/stat)    r=$(LC_MESSAGES=C chrt -p $$ | sed -n "s,^.*priority: ,,p")    case $r in      3) c="IDLE_PRIORITY_CLASS" ;;      9) c="BELOW_NORMAL_PRIORITY_CLASS" ;;      15) c="NORMAL_PRIORITY_CLASS" ;;      21) c="ABOVE_NORMAL_PRIORITY_CLASS" ;;      27) c="HIGH_PRIORITY_CLASS" ;;      32) c="REALTIME_PRIORITY_CLASS" ;;      *) c="?" ;;    esac    printf "nice -n %3d:%5d %5d %5d %5d %s\\n" \           "'$i'" "$n" "$s" "$p" "$r" "$c"  ' done -- Regards, Christian -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
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