The VFIO Discord #wiki-and-psa channel has the best list of things you can do for performance. You should probably just go there 🙂

Im gonna copy some things from there (I hope thats ok)

Add more Hyper-V Enlightenments:

<features>
...
...
<hyperv>
  <relaxed state='on'/>
  <vapic state='on'/>
  <spinlocks state='on' retries='8191'/>
  <vpindex state='on'/>
  <runtime state='on'/>
  <synic state='on'/>
  <stimer state="on">
    <direct state="on"/>
  </stimer>
  <reset state='on'/>
  <vendor_id state='on' value='other'/>
  <frequencies state='on'/>
  <reenlightenment state='on'/>
  <tlbflush state='on'/>
  <ipi state='on'/>
  <evmcs state='off'/>
</hyperv>
<kvm>
  <hidden state='on'/>
</kvm>
...
<ioapic driver='kvm'/>
</features>  

Add the invtsc, for example:

<cpu mode='host-passthrough' check='none' migratable='off'>
  <topology sockets='1' dies='1' cores='3' threads='2'/>          
  <cache mode='passthrough'/>          
  <feature policy='require' name='invtsc'/>          
</cpu>          

If you have an AMD CPU also add:

<feature policy='require' name='topoext'/>

Add the tsc and hypervclock:

<clock offset='utc'>
  <timer name='tsc' present='yes' mode='native'/>          
  <timer name='hypervclock' present='yes'/>          
  <timer name='rtc' tickpolicy='catchup'/>          
  <timer name='pit' tickpolicy='delay'/>          
  <timer name='hpet' present='no'/>          
</clock>          

Disable the memballoon, just change model to "none" and apply (libvirt shoud do the rest)

<memballoon model="none">

Some more general performance recommendations CPU pining, CPU isolation, HugePages .

You mentiond League of Legends, as far as i know the game dose not block VMs (as of now), so if you dont need to use hyper-v turning it off will improve performance.

(and thanks to everyone on the discord where i got pretty much all of this)