Windows 10: Slow download speed after creating External Virtual Switch


  1. Posts : 13
    Windows 10 Pro x64 v1703
       30 Oct 2017 #1

    Slow download speed after creating Hyper-V External Virtual Switch


    Hello.
    After buying a new PC (its specs are on my profile), enabling Hyper-V and creating a new External Virtual Switch, I notice that the download speed drops dramatically. My internet conneciton is 1Gbps down and 200Mbps up.

    Without External Virtual Switch:

    Click image for larger version. 

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    • Iperf with a host on the same LAN (upload 911Mbps, download 777Mbps):

    Click image for larger version. 

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ID:	161304
    Click image for larger version. 

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    • Lan Speed test (746 Mbps upload and 716 Mbps download):

    Click image for larger version. 

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ID:	161306

    With External Virtual Switch:


    • CPU usage while on Speedtest (notice the first core is fully maxed out):

    Click image for larger version. 

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ID:	161308

    • Lan Speed Test (742 Mbps upload and 596Mbps download):

    Click image for larger version. 

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Views:	34 
Size:	12.9 KB 
ID:	161320

    • Iperf with a host on the same LAN (upload 861 Mbps, download 583 Mbps):

    Click image for larger version. 

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Views:	34 
Size:	39.4 KB 
ID:	161323
    Click image for larger version. 

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ID:	161326

    • CPU usage while on Iperf (download) - Notice, once again, Core 1 fully maxed out​:

    Click image for larger version. 

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ID:	161325


    Conclusion

    When the External Virtual Switch is enabled, I assume the download speed is lower due to the fact one CPU core is being maxed out, my question is why? Why isn't the load spread throughout the cores?
    Is anyone experiencing a similar issue?

    Regards.
    Last edited by Portugal; 30 Oct 2017 at 20:34.
      My ComputerSystem Spec

  2.    31 Oct 2017 #2

    I have the exact same problem.
    Any help would be appreciated.
      My ComputerSystem Spec

  3.    01 Nov 2017 #3

    Portugal said: View Post
    Hello.
    After buying a new PC (its specs are on my profile), enabling Hyper-V and creating a new External Virtual Switch, I notice that the download speed drops dramatically. My internet conneciton is 1Gbps down and 200Mbps up.

    Without External Virtual Switch:

    Click image for larger version. 

Name:	image.png 
Views:	3 
Size:	576.1 KB 
ID:	161309

    • Iperf with a host on the same LAN (upload 911Mbps, download 777Mbps):

    Click image for larger version. 

Name:	image.png 
Views:	36 
Size:	40.7 KB 
ID:	161304
    Click image for larger version. 

Name:	image.png 
Views:	36 
Size:	37.5 KB 
ID:	161305


    • Lan Speed test (746 Mbps upload and 716 Mbps download):

    Click image for larger version. 

Name:	image.png 
Views:	36 
Size:	12.9 KB 
ID:	161306

    With External Virtual Switch:


    • CPU usage while on Speedtest (notice the first core is fully maxed out):

    Click image for larger version. 

Name:	image.png 
Views:	3 
Size:	102.5 KB 
ID:	161308

    • Lan Speed Test (742 Mbps upload and 596Mbps download):

    Click image for larger version. 

Name:	image.png 
Views:	34 
Size:	12.9 KB 
ID:	161320

    • Iperf with a host on the same LAN (upload 861 Mbps, download 583 Mbps):

    Click image for larger version. 

Name:	image.png 
Views:	34 
Size:	39.4 KB 
ID:	161323
    Click image for larger version. 

Name:	image.png 
Views:	34 
Size:	37.7 KB 
ID:	161326

    • CPU usage while on Iperf (download) - Notice, once again, Core 1 fully maxed out​:

    Click image for larger version. 

Name:	image.png 
Views:	3 
Size:	110.6 KB 
ID:	161325


    Conclusion

    When the External Virtual Switch is enabled, I assume the download speed is lower due to the fact one CPU core is being maxed out, my question is why? Why isn't the load spread throughout the cores?
    Is anyone experiencing a similar issue?

    Regards.
    Have you set the number of cores to 8 in hyer-v settings (virtual processor). No idea otherwise.
      My ComputerSystem Spec

  4.    01 Nov 2017 #4

    As of 1709 a Default Switch is created so you may not need an external switch.

    Details about the Default Switch

    The switch named “Default Switch” or “Layered_ICS”, allows virtual machines to share the host’s network connection. Without getting too deep into networking (saving that for a different post), this switch has a few unique attributes compared to other Hyper-V switches:
    • Virtual machines connected to it will have access to the host’s network whether you’re connected to WIFI, a dock, or Ethernet.
    • It’s available as soon as you enable Hyper-V – you won’t lose internet setting it up.
    • You can’t delete it.
    • It has the same name and device ID (GUID c08cb7b8-9b3c-408e-8e30-5e16a3aeb444) on all Windows 10 hosts so virtual machines on recent builds can assume the same switch is present on all Windows 10 Hyper-V host.
    Hyper-V virtual machine gallery and networking improvements | Virtualization Blog

    You could try that instead (upgrade from 1703 to 1709 and delete external switch) - I don't see this issue on 1709 but then my connection is perhaps too slow (100 Mbps up/down).
      My ComputerSystem Spec


  5. Posts : 13
    Windows 10 Pro x64 v1703
    Thread Starter
       01 Nov 2017 #5

    cereberus said: View Post
    Have you set the number of cores to 8 in hyer-v settings (virtual processor). No idea otherwise.
    Hello cereberus.
    I was not clear in my first post. The slow download speed is not a problem of a virtualized OS, but the Windows original installation. The speed drops as soon as I enable the External Virtual Switch.
    lx07 said: View Post
    As of 1709 a Default Switch is created so you may not need an external switch.
    Hyper-V virtual machine gallery and networking improvements | Virtualization Blog
    You could try that instead (upgrade from 1703 to 1709 and delete external switch) - I don't see this issue on 1709 but then my connection is perhaps too slow (100 Mbps up/down).
    Hello lx07, I already have the 1709, but form what I've read so far, the thing with the Default switch is it used NAT, and I want my VM's to have access to my internal network.

    Regards.
      My ComputerSystem Spec

  6.    02 Nov 2017 #6

    Portugal said: View Post
    I already have the 1709, but form what I've read so far, the thing with the Default switch is it used NAT, and I want my VM's to have access to my internal network.
    That is true.

    There are a couple of suggestions here if you didn't see it already - either disable VMQ on the NIC or make sure RSS Base processor number is set to 0.

    server 2012 hyper-v vSwitch performance is terrible
      My ComputerSystem Spec


  7. Posts : 13
    Windows 10 Pro x64 v1703
    Thread Starter
       02 Nov 2017 #7

    lx07 said: View Post
    That is true.

    There are a couple of suggestions here if you didn't see it already - either disable VMQ on the NIC or make sure RSS Base processor number is set to 0.

    server 2012 hyper-v vSwitch performance is terrible
    Hello lx07, my NIC does not support VMQ, even using powershell :-(

    Regards.
      My ComputerSystem Spec


 

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