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Date: Sat, 14 Oct 2023 09:47:18 -0400
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Subject: Re: Run a Cygwin process with "higher" scheduler priority
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To: Cedric Blancher <cedric.blancher@gmail.com>, cygwin@cygwin.com
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From: Eliot Moss via Cygwin <cygwin@cygwin.com>
Reply-To: Eliot Moss <moss@cs.umass.edu>
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On 10/14/2023 7:39 AM, Cedric Blancher via Cygwin wrote:
> On Fri, 11 Aug 2023 at 19:14, Brian Inglis <Brian.Inglis@shaw.ca> wrote:
>>
>> On 2023-08-11 09:44, Cedric Blancher via Cygwin wrote:
>>> How can we set the scheduler priority for a Cygwin process to "higher"
>>> than normal on start?
>>>
>>> Basically we want a Cygwin compatible script version of the Windows
>>> task manager feature Name/PID--->Details--->Set priority--->Higher
>>
>> Pretend the system is BSD or Linux and web search e.g. SO for that capability,
>> facility, or feature, then check Cygwin with Search Packages or:
>>
>> $ cygcheck -p usr/bin/nice
>> Found 6 matches for usr/bin/nice
> 
> I know about nice and renice, but I don't see whether it is working or not.
> 
>> coreutils-debuginfo-8.26-2 - coreutils-debuginfo: Debug info for coreutils
>> ...
>> coreutils-9.0-1 - coreutils: GNU core utilities (includes fileutils, sh-utils
>> and textutils)
>> $ cygcheck -p usr/bin/renice
>> Found 6 matches for usr/bin/renice
>> util-linux-debuginfo-2.32.1-1 - util-linux-debuginfo: Debug info for util-linux
>> util-linux-debuginfo-2.33.1-1 - util-linux-debuginfo: Debug info for util-linux
>> util-linux-debuginfo-2.33.1-2 - util-linux-debuginfo: Debug info for util-linux
>> util-linux-2.32.1-1 - util-linux: Collection of basic system utilities
>> util-linux-2.33.1-1 - util-linux: Collection of basic system utilities
>> util-linux-2.33.1-2 - util-linux: Collection of basic system utilities
>> $ 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.
> 
>>
>> 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.

Best - EM

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