[SOLVED] VM is very slow after P2V and Passthrough PCI

Homer-S

New Member
Nov 18, 2020
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Hello community,

I moved recently my physical Ubuntu server to a Proxmox VM. Server is working but access to Web Services like Nextcloud or Wordpress is very very slow. It seems something is slowing the server down.

I hope you can help me searching for the root cause.

Setup:
1606028298865.png


DMESG attached


Thank you for helping a new Proxmox user.
 

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May 31, 2020
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virtio_balloon virtio0: Out of puff! Can't get 1 pages seems to indicate that your system is running low on memory. Maybe trying to reclaim memory is slowing it down?
Maybe you could try the VM without ballooning or try setting the minimum to 6.00 GiB also?
Maybe enabling USB3 for the USB passthrough devices might help? If I don't enable USB3, my USB-keyboard regularly drops some key presses.
Are you sure there is no other network devices with the same MAC-address on the network? Losing and resubmitting packets can cause a slow down.
 

Homer-S

New Member
Nov 18, 2020
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I followed your great hints.
Important one was to delete old entry in router from old physical machine. Now it is faster but still not the max it could be.

Copying a large file is reaching on a 1Gb cable connection between 50 and 75MB/sec. On my old setup it was up to 120.
Is this the virtualization "issue" or is there something wrong. Where should I have a look?

Network settings of the node:
1606049801979.png
 

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  • latest-dmesg.txt
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May 31, 2020
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Can you give more information about the host system? If it has only 4 cores, maybe 4 cores for the VM is too much. Or maybe 6GB RAM is reducing your host disk cache?
Are you sure you are not reading and writing to the same physical disk (now that you are using VMs)? This could cause the speed to be half as you are doubling the number of operations to the disk.
You could try VirtIO SCSI single for the SCSI controller, which might enable more parallelism for your I/O operations. You could try enabling caching for your (virtual) disks.
 

Homer-S

New Member
Nov 18, 2020
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The host is powered by a i7-8700t 6 cores/12 Threats 16GB RAM
currently running 2 VMs (6Cores/4GB///4Cores/6GB)

Speed issues are with a passthrough HDD dedicated to this VM so normally no double access.

In the meanwhile I changed NIC/Vmbrs to this and reached a speed improvement but it is still not close to max transfer rate.
1606078029993.png
 
May 31, 2020
120
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the Netherlands
You are allocating 10 virtual cores to the VMs, while you have only 12 actual threads. Please note that I/O and background Proxmox processes also (want to) use some threads.
In my experience with Intel, the hyper-threads don't give twice the performance (more like 30% extra). It does appear to be more responsive, but only if the other thread is waiting on something.
Can you try with 3 and 2 virtual cores (instead of 6 and 4), in order to free up some more threads for both disk (use VirtIO SCSI Single to make use of this) and network I/O?
 

Homer-S

New Member
Nov 18, 2020
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Hello AVW,

I changed it acc your suggestions and it is now running really as expected and smoothly. I love it!

To sum up, I guess biggest issue had been thenetwork issue mentioned in your first post and the combination of reducing a little addressed resources and change to VirtIO SCSI single (I did not test it one by one)

Thanks!!!
 
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