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Re: [Xen-users] Not good performance on Xen

On 24/10/17 02:18, Berillions wrote:

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 :

Xen Benchmark :

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?

I think you will definitely want to reserve at least 2 cores for the dom0, just like you reserved 6GB RAM.

In addition, as others have mentioned, cpu pinning will probably also help, but first step is to not share cores between the dom0 and the domU, as the dom0 also needs to do some work to allow the domU to work.

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