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Re: [Xen-devel] HVM guest performance regression

On Fri, 2017-05-26 at 18:14 +0200, Juergen Gross wrote:
> Looking for the reason of a performance regression of HVM guests
> under
> Xen 4.7 against 4.5 I found the reason to be commit
> c26f92b8fce3c9df17f7ef035b54d97cbe931c7a ("libxl: remove
> freemem_slack")
> in Xen 4.6.
> The problem occurred when dom0 had to be ballooned down when starting
> the guest. The performance of some micro benchmarks dropped by about
> a factor of 2 with above commit.
Performance of micro benchmarks run _inside_ the guest, I'm guessing?

> Interesting point is that the performance of the guest will depend on
> the amount of free memory being available at guest creation time.
> When there was barely enough memory available for starting the guest
> the performance will remain low even if memory is being freed later.
OOC, what kind of host? Big? Small? NUMA, non-NUMA?, etc

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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