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Re: [vfio-users] Speed tips requested

Assuming you use libvirt, make sure to use vCPU pinning. For disk access, try cache='writeback' io='threads'. If you switch to scsio-vfio, this will give you the ability to define queue length which might additionally improve IO. Also, try QCOW2 format for guest disk, it might enable some additional optimizations. However given you host seem to have little spare capacity, YMMV


  Original Message  
From: Patrick O'Callaghan
Sent: Sunday, 26 March 2017 09:25
To: vfio-users redhat com
Subject: [vfio-users] Speed tips requested

I'm running Windows 10 in a KVM/QEMU VM under Fedora 25. The host is a
16GB i3770 and I have 4 threads (2 cores) dedicated to the VM with CPU
pinning and 8GB hugepages. The passthrough GPU is an Nvidia Geforce GTX

The guest disk is a 100GB raw file under vfio. The host disk is a 1TB
Toshiba SATA 2.

This generally works quite well, except for two things:

1) KB events seem to overrun in games, i.e. there is stuttering and a
buzz when holding down a key for too long. Keyboard and mouse are
wireless Logitech hardware on a USB-2 port.

Initially I had configured USB-2 on the VM and in an effort to fix this
changed it to USB-3, which seemed to make it slightly faster but not go
away (nb: this is still on the same physical USB-2 port).

I then attempted to enable MSI as outlined in https://vfio.blogspot.co.
uk/2014/09/vfio-interrupts-and-how-to-coax-windows.html. After the USB-
3 change (see above) Windows now shows the USB-3 controller as using
MSI, however the Windows Nvidia drivers don't seem to support it, even
after registry editing. Note that the GPU hardware does support it
according to Linux ('lspci -v -s <id>').

2) There is quite frequent (every few seconds) visual stuttering --
pause then continue -- when moving rapidly through a rendered scene,
possibly caused by disk I/O.

I'm already using vfio. Would vfio-scsi make a difference? Should I be
thinking about a dedicated disk?

Thanks for any hints.


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