Re: [Xen-devel] Xen 4.5 development update (July update)

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On ven, 2014-08-15 at 13:23 -0400, konrad.wilk@xxxxxxxxxx wrote:

> = Open =

> == x86 == 

> *  HT enabled, virtualization overhead is high (Xen 4.4) (none)
>    kernbench demonstrated it
>    Looking and tracing
>    http://www.gossamer-threads.com/lists/xen/devel/339409
>   -  Dario Faggioli
> 
Mmm... I realize only now that I must have missed your last email about
this... So, sorry.

In any case, didn't we settle on closing it? The bullet is here because
very high perf degradation between baremetal and HVM DomU was seen when
running `kernbench -j' (i.e., kernbench with unlimited number of build
jobs) with HT enabled.

Both me and other people tried to reproduce the issue, and here's the
number:

HT Enabled
==========
                 Host               Guest
kernbench -j4    31.598 (0.113666)  34.078 (0.168582)
kernbench -j8    26.676 (0.16772)   26.672 (0.0432435)
kernbench -j     27.674 (0.933584)  27.49 (0.364897)

To me, this means we don't have an issue of high virtualization overhead
when HT is enabled (look at the last row!).

All the other things that came up in previous threads are not to be
ignored or forgot, of course, and I won't, but they don't have anything
to do with this.

Let me know,
Dario

-- 
<<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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