[vfio-users] Eliminate Mini Stutter in "Witcher 3: The Wild Hunt" on top of KVM/VFIO

[Piotr Szymaniak]

On Wed, Mar 16, 2016 at 11:25:30AM +0700, Okky Hendriansyah wrote:
> Hi All,
> 
> I experienced a very noticeable mini stutters here and there when playing
> "Witcher 3: The Wild Hunt" on my Windows 10 VM with OVMF and MSI enabled. I
> was using the official linux-lts-4.1.19-1 from Arch Linux repository.
> Apparently after changing these 3 kernel configurations and recompile the
> kernel, the mini stutter issues are gone!

Hi,

Got the same issues (with older game, but it was the first one to try
after successfull passthru) and with mentioned changes they were fixed.


> Here are the kernel configuration that I changed:
> 1.) 1000 MHz clock resolution

I was looking at this before, diffing friends config. But your post was
here right after this, so I've changed (changes and update from 4.4.4 to
4.4.6):
# diff -Naur /boot/config-4.4.4 /boot/config-4.4.6 | grep HZ
-CONFIG_HZ_300=y
-# CONFIG_HZ_1000 is not set
-CONFIG_HZ=300
+# CONFIG_HZ_300 is not set
+CONFIG_HZ_1000=y
+CONFIG_HZ=1000


> 2.) Voluntary preemption scheduling

# diff -Naur /boot/config-4.4.4 /boot/config-4.4.6 | grep PREEMPT
-CONFIG_PREEMPT_RCU=y
 CONFIG_PREEMPT_NOTIFIERS=y
 # CONFIG_PREEMPT_NONE is not set
-# CONFIG_PREEMPT_VOLUNTARY is not set
-CONFIG_PREEMPT=y
-CONFIG_PREEMPT_COUNT=y
+CONFIG_PREEMPT_VOLUNTARY=y
+# CONFIG_PREEMPT is not set
-CONFIG_DEBUG_PREEMPT=y


> 3.) Madvise hugepages (not really sure that this changes anything actually)

Didnt touch hugepages.


My two cents about success story: passthru with i5-2400 on Intel DQ67SW
motherboard and Radeon HD 4890 with Windows 7 (using ovmf).


Piotr Szymaniak.
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