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Hi Maxime,

Maybe it's related to vcpu scheduling and load balancing, as you mentioned 8 vcpus provided better performance.

Could you try to:

1) pin those 10 guest vpcus to 6-15 (in vm configuration, set cpus="6-15")

2) pin dom0's vcpus to 0- 3.

add 'dom0_max_vcpus=4 dom0_vcpus_pin' to your kernel cmd line;

use 'xl vcpu-pin' to manually pin dom0's vcpus after bootting into dom0.

(if dom0 needs more cores then you can just change the number accordingly)

Best,

Kenneth

On Wed, Oct 25, 2017 at 7:53 AM Berillions <berillions@xxxxxxxxx> wrote:

Hi,

I create a Windows 10 VM (HVM) with Xen. I passed on my VM this device :
- AMD Rx480 - 8 Go

About CPU and Memory, i passed all my cores (16 cores) from my Ryzen (1700X). My system has 16Gb of Memory RAM and i passed 10Gb for the Guest, the host have 4Gb only (dom0_mem=4000M,max:4000M).

I installed "Rise of Tomb Raider" and i launch a benchmark on Win10 on Xen and Win10 BareMetal (installed really on my Desktop). With the same graphic options, the performance decrease on Xen compared to BareMetal.

Bare Metal Benchmark :
https://cdn.discordapp.com/attachments/352637536935346187/371588269231570944/RottR_Benchmark_BM.jpg

Xen Benchmark :
https://media.discordapp.net/attachments/352637536935346187/371588325015814155/RottR_Benchmark_Xen.jpg?width=400&height=225

The average FPS is not bad on Xen, i lost only 4FPS. But if you see the "minimal FPS", there are a big differences :
31FPS for Xen, 51 for BareMetal for the 1st test
7FPS for Xen, 21FPS pour BareMetal for the 2nd and 3rd test)

I remarked something between Xen and Bare Metal.
- During the test #2 (Syria) i have slowdown on Xen. But not on BM.
- During the test #3 (Geothermal Valley), there are missing texture on Xen and not on BM

To have early the same perf, no slowdown and missing texture, i must to set 8 vcpus to the Guest

What can be the causes of these performance losses?

Thanks,
Maxime
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Re: [Xen-users] Not good performance on Xen