Re: [Xen-devel] HVM guest performance regression

2017-05-26 Thread Juergen Gross 
On 26/05/17 19:04, Dario Faggioli wrote:
> 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?

Yep. libmicro benchmark "munmap".

>> 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

I've tested this to happen _always_ on my laptop (Dual core Intel(R)
Core(TM) i7-4600M CPU @ 2.90GHz, 8GB memory, non-NUMA).

Guest size was 2GB, 1 vcpu.


Juergen

___
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel

Re: [Xen-devel] HVM guest performance regression

2017-05-26 Thread Dario Faggioli 
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

Regards,
Dario
-- 
<> (Raistlin Majere)
-
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R Ltd., Cambridge (UK)

signature.asc
Description: This is a digitally signed message part
___
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel