Troubleshooting VM performance
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Troubleshooting VM performance

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Article ID: 419238

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Updated On:

Products

VMware vSphere ESXi

Issue/Introduction

This article goes through how to identify and troubleshoot VM performance:

  • The guest operating system boots slowly
  • Applications running in virtual machines perform poorly
  • Applications running in virtual machines take a long time to launch
  • Applications running in virtual machines frequently become unresponsive

Environment

VMware vSphere ESXI 

Cause

Due to insufficient resources, the VM was unable to handle the traffic load, resulting in buffer exhaustion.

Resolution

 To determine performance issue is it due to cpu, memory or networking constraints:    

 

  1. ESXTOP overview for Performance Troubleshooting

  2. CPU - esxtop > press 'c'

    Field Value Description
    %USED N/A CPU Core cycles used by a VM. High values are an indicator for VMs causing performance problems on E SXi Hosts.
    %SWPWT ≥ 5 Counter showing how long a VM has to wait for swapped pages read from disk. A reason for this could be memory overcommitment.
    Pay attention if %SWPWT is >5!
    %MLMTD ≥ 1 Counter showing percentage of time a ready to run vCPU was not scheduled because of a CPU limit setting. Remove the limit for better performance.
    %CSTP ≥ 3 This value is interesting if you are using vSMP virtual machines. It shows the percentage of time a ready to run VM has spent in co-deschedule state.
    If value is >3 decrease the number of vCPUs from the VM concerned.
    %RDY ≥ 10 Percentage of time a VM was waiting to be scheduled.If you note values between five and ten percent take care.
    Possible reasons: too many vCPUs, too many vSMP VMs or a CPU limit setting (check %MLMTD)

    Note: Keep a close eye on the RDY as this is related to the Scheduler, due the bigger the value the Scheduler is the longer it will take to respond or process something.


  3.  Memory - esxtop > press 'm'


    Field Value Description
    MCTLSZ ≥ 1 Amount of guest physical memory (MB) the ESXi Host is reclaiming by balloon driver. A reason for this is memory overcommitment.
    ZIP/s ≥ 1 Values larger 0 indicate that the host is actively compressing memory.
    UNZIP/s Values larger 0 indicate that the host is accessing compressed memory.
    Reason for this behaviour is memory overcommitment.
    CACHEUSD ≥ 1 Memory (in MB) compressed by ESXi Host
    SWCUR: ≥ 1 Memory (in MB) that has been swapped by VMKernel.
    Possible cause: memory overcommitment.
    SWR/s, SWW/s: ≥ 1 Rate at which the ESXi Host is writing to or reading from swapped memory.
    Possible cause: memory overcommitment.

  4. Network - esxtop > press 'n'

    Field Value Description
    %DRPTX ≥ 1 Dropped Packages transmitted/Dropped Packages received.
    Values larger 0 are a sign for high network utilization
    %DRPRX
    Used-by/Team-PNIC N/A provide information what physical NIC a VM is actually using

  5. virtual nic buffers

Note: Memory equals buffers and CPU equals speed which we move data, if we are unable to process the amount of buffers being sent by the application those will be going out of buffer or dropping which is going to be causing slowness on the performance. If that is the Case Increase the amount of CPU and memory.
Note: If this is is a third party application, reach out to the vendor so they can preform the changes require to make it work better.

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