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--- linux:server:windows_vm [2022/09/17 18:00] – add updates section michaelbromilow
+++ linux:server:windows_vm [2023/09/04 21:08] (current) – add more hyperv enlightenments michaelbromilow
@@ Line 30: / Line 30: @@
 Useful commands to debug some of this:
-  * ''# perf kvm --host top -p `pidof qemu-system-x86_64`''
+  * ''# perf kvm %%--%%host top -p `pidof qemu-system-x86_64`''
     * Shows how often qemu is executing various functions, ''[k]'' for kernel space and ''[.]'' for user space.
     * There is also one function used for making the switch to guest space and it accounts for all time spent there. On a 4.14 kernel with intel cpu that function is ''vmx_vcpu_run'' but it might differ.
-  * ''# perf stat -e 'kvm:*' -a -- sleep 1''
+  * ''# perf stat -e 'kvm:*' -a %%--%% sleep 1''
     * This should show the reason a VM is doing ''VM_EXIT''. Values should be roughly "less than 1000".
-  * ''# perf kvm --host stat live''
+  * ''# perf kvm %%--%%host stat live''
     * This one should show what the VM is doing? Apparently most time % should be ''HLT'' otherwise it's not idle.
     * High ''HLT'' time indicates the machine is waking up and going to sleep a lot (context switching?).
 It may also be a good idea to use ''powercfg'' to find out why the OS is waking up lots, if it is.
+===== Tweaks for performance =====
+See https://libvirt.org/formatdomain.html and [[https://leduccc.medium.com/improving-the-performance-of-a-windows-10-guest-on-qemu-a5b3f54d9cf5|this guide]].
+==== CPU Topology & Configuration ====
+Match the host CPU topology with the VM (cores can be changed as desired). Enable ''host-passthrough'' to disable CPU emulation as much as possible.
+  <domain type="kvm">
+    ...
+    <cpu mode="host-passthrough" check="none" migratable="on">
+      <topology sockets="1" dies="1" cores="3" threads="2"/>
+    </cpu>
+    ...
+  </domain>
+Add one or more threads dedicated to I/O (libvirt recommends max 1 per core).
+  <domain type="kvm">
+    ...
+    <iothreads>1</iothreads>
+    ...
+  </domain>
+Set up the vCPUs for the guest by pinning them to the host. See ''virsh capabilities''. Note that Intel CPU sets are specified as e.g. (0,4); (1,5); (2,6); (3,7) for a 4-core CPU (i.e. the threading is split across the bottom and top halves of the cpuset range). For example this is how I set up the i7-3770 keeping core 0 for emulation/io/host.
+  <domain type="kvm">
+    ...
+    <vcpu placement="static">6</vcpu>
+    <cputune>
+      <vcpupin vcpu="0" cpuset="1"/>
+      <vcpupin vcpu="1" cpuset="2"/>
+      <vcpupin vcpu="2" cpuset="3"/>
+      <vcpupin vcpu="3" cpuset="5"/>
+      <vcpupin vcpu="4" cpuset="6"/>
+      <vcpupin vcpu="5" cpuset="7"/>
+      <emulatorpin cpuset="0,4"/>
+      <iothreadpin cpuset="0,4"/>
+    </cputune>
+    ...
+  </domain>
 ==== Enlightenments ====
@@ Line 52: / Line 92: @@
     <pae/>
     <hyperv>
-      <relaxed state='on'/>
+      <relaxed state="on"/>
-      <vapic state='on'/>
+      <vapic state="on"/>
-      <spinlocks state='on' retries='8191'/>
+      <spinlocks state="on" retries="8191"/>
-      <vpindex state='on'/>
+      <vpindex state="on"/>
-      <synic state='on'/>
+      <runtime state="on"/>
-      <stimer state='on'/>
+      <synic state="on"/>
-      <reset state='on'/>
+      <stimer state="on"/>
+      <reset state="on"/>
       <vendor_id state="on" value="KVM Hv"/>
       <frequencies state="on"/>
+      <reenlightenment state="on"/>
+      <tlbflush state="on"/>
+      <ipi state="on"/>
+      <evmcs state="on"/>
     </hyperv>
   </features>