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UV 11.2.5 / RHEL 7 : Phantoms suddenly running with 'NICE' of 2

  • May 6, 2021
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We have a strange situation occurring where a phantom process (launched using the UV PHANTOM command) somehow have their linux 'nice' value set to 2. This results in the processes running at a slightly higher (less important) priority of 22.

We have no linux scripts that are triggering this, and the command launched does not 'renice' itself so are at a loss to explain how this is happening.

Is there anything within UV that will result in a phantom process having it's 'NICE' value adjusted to reduce the PID's impact?
Is anyone aware of anything within RHEL that could also lead to a process being automatically reniced this way?

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Gregor Scott
Software Architect
Pentana Solutions
Mount Waverley VIC Australia
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    6 replies

    Jonathan Smith
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    • Jonathan SmithRocketeer
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    • May 6, 2021
    We have a strange situation occurring where a phantom process (launched using the UV PHANTOM command) somehow have their linux 'nice' value set to 2. This results in the processes running at a slightly higher (less important) priority of 22.

    We have no linux scripts that are triggering this, and the command launched does not 'renice' itself so are at a loss to explain how this is happening.

    Is there anything within UV that will result in a phantom process having it's 'NICE' value adjusted to reduce the PID's impact?
    Is anyone aware of anything within RHEL that could also lead to a process being automatically reniced this way?

    ------------------------------
    Gregor Scott
    Software Architect
    Pentana Solutions
    Mount Waverley VIC Australia
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    Both Universe and UniData automatically change the nice value of a phantom when it's spawned. As Phantoms are viewed as background processing they are given a lower priority.

    Thanks
    Jonathan Smith
    UniData  ATS and Principal Engineer 

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    • Gregor Scott
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    • May 7, 2021
    Both Universe and UniData automatically change the nice value of a phantom when it's spawned. As Phantoms are viewed as background processing they are given a lower priority.

    Thanks
    Jonathan Smith
    UniData  ATS and Principal Engineer 

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    That is interesting, as it contradicts our experience  with phantoms on UV.
    Until now, we have never had a phantom process automatically change it's priority.
    Even now, it is only some of our phantoms that his happens to.


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    Gregor Scott
    Mount Waverley VIC Australia
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    Jonathan Smith
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    • Jonathan SmithRocketeer
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    • 356 replies
    • May 7, 2021
    That is interesting, as it contradicts our experience  with phantoms on UV.
    Until now, we have never had a phantom process automatically change it's priority.
    Even now, it is only some of our phantoms that his happens to.


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    Gregor Scott
    Mount Waverley VIC Australia
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    Hi Gregor,

    I will double check this for you as it has always been our understanding internally that phantoms are reniced to a lower priority when they are launched.

    Thanks,
    Jonathan

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    Jonathan Smith
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    Jonathan Smith
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    • Jonathan SmithRocketeer
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    • 356 replies
    • May 7, 2021
    Hi Gregor,

    I will double check this for you as it has always been our understanding internally that phantoms are reniced to a lower priority when they are launched.

    Thanks,
    Jonathan

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    Jonathan Smith
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    Hi Gregor,

    I've done some checking and testing on our internal systems for both UV and UD and it would appear that the nice values for phantoms are not changed when a phantom is spawned. I will look into this further in the next few weeks as it has been a widely held belief internally that the nice values were changed when a phantom was spawned and will correct any internal misunderstandings based on those findings.

    Thanks,
    Jonathan



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    Jonathan Smith
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    • Anonymous
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    • May 7, 2021
    We have a strange situation occurring where a phantom process (launched using the UV PHANTOM command) somehow have their linux 'nice' value set to 2. This results in the processes running at a slightly higher (less important) priority of 22.

    We have no linux scripts that are triggering this, and the command launched does not 'renice' itself so are at a loss to explain how this is happening.

    Is there anything within UV that will result in a phantom process having it's 'NICE' value adjusted to reduce the PID's impact?
    Is anyone aware of anything within RHEL that could also lead to a process being automatically reniced this way?

    ------------------------------
    Gregor Scott
    Software Architect
    Pentana Solutions
    Mount Waverley VIC Australia
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    Gregor,

    Check if this behaves differently depending upon whether UniVerse is started from systemctl or manually using uv -admin -start at a command prompt. There does seem to be difference in the way that Linux services set the relative priority of child processes launched from systemctl - I think it is called a 'process group'. From an initial review it looks like all processes started from the same process leader (i.e. a 'process group') might share the same resource allocation.

    This would be an interesting topic to prove or disprove. If proven then I understand that the systemctl behavior can be modified in Linux.

    Regards
    JJ

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    John Jenkins
    Principal Technical Support Engineer
    Rocket Software Limited
    U.K.
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    • Gregor Scott
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    • June 6, 2021
    We have a strange situation occurring where a phantom process (launched using the UV PHANTOM command) somehow have their linux 'nice' value set to 2. This results in the processes running at a slightly higher (less important) priority of 22.

    We have no linux scripts that are triggering this, and the command launched does not 'renice' itself so are at a loss to explain how this is happening.

    Is there anything within UV that will result in a phantom process having it's 'NICE' value adjusted to reduce the PID's impact?
    Is anyone aware of anything within RHEL that could also lead to a process being automatically reniced this way?

    ------------------------------
    Gregor Scott
    Software Architect
    Pentana Solutions
    Mount Waverley VIC Australia
    ------------------------------
    Just following up on this discussion in case anyone has been watching it.

    We tracked down the root cause to application coding which had been attempting to adjust the Linux PID's "nice" value but got it's logic wrong.

    So it was nothing to do with UV automatically adjusting the PID priority, and all to do with "Oh yea, we coded that - it's broken".

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    Gregor Scott
    Software Architect
    Pentana Solutions
    Mount Waverley VIC Australia
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