Notes on turbo with XenServer 7

Hi!

CPU turbo mode is important for performance, especially with the increased turbo spans since AVX 2.0 was introduced a couple of years ago (Haswell).

Turbo mode is also a bit tricky when it comes to XenServer configuration and that’s been a good reason for using CPUs with a high base frequency instead. The top models for base frequency consume a lot of power however and have only been available with workstation models.

If I understand the below blog post correctly utilizing AVX 2 has in fact been a restriction in PV guests and introducing HVM guests in XenServer 7 now supports AVX 2 (among other things).

https://www.citrix.com/blogs/2016/06/30/xenserver-7-building-the-foundations-of-a-great-future/

In sum, the move from Xen 4.4 (XenServer 6.5) to Xen 4.6 (XenServer 7.0) provides better support for AVX 2 turbo (Intel Haswell or later, i.e. most servers 2 years old or newer).

It does, however, require that the server is not pooled with any server that has older CPUs as that would impact the pool feature level.

There should be a lot of XenServer servers out there with low base frequency haswell CPUs and high turbo spans as that has been pushed forward by most of the OEMs as far as I’ve seen. It wouldn’t be unlikely then if a lot of those customers are also hurting from bad performance due to limited turbo support and/or complex configuration requirements.

Then again, perhaps I’m missing something. Any comments on this from the GRID team or anyone else? Have you noticed if turbo on haswell servers seems to perform better with XenServer 7 than previously?

Hi Tony,

I haven’t heard anything either way but will ping the XenSever team. the best place to ask is probably on the XenServer GPU forum: http://discussions.citrix.com/forum/523-gpu-technologies/

Anecdotally I heard that turbo didn’t frequently kick in on older XenServer’s but there is plenty of advice on how to correctly configure so it can http://support.citrix.com/article/CTX200390

Best wishes,
Rachel

Hi Rachel

Thank you, if you (or anyone else) receive any updates it would be interesting to know. I’ll update as well of course if I hear anything and/or get the time during the summer to run the tests in the lab.

Thanks
Tony