Re: Lost of performance over AMD-V with KVM?

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jul 09, 2013 at 04:31:32PM +0200, Victor fernandez wrote:
> Hi Gleb,
> 
>     there are flags that with the tuning of KVM (-cpu host) we get
> that some of
>     important cpu flags are not included in SL6 ( Ht, rdtscp,
> 3dnowext, 3dnow,
> constant_tsc,nonstop_tsc,amd_dcm,monitor,svm,extapic,osvw,ibs,skinit,wdt,nodeid_msr).
> 
Not all of them will be passed to a guest even with -cpu host, but
instruction set related once like 3dnowext/3dnow you should be.

What is qemu command line that you use? 

>     And the machines used for testing were 2 nodes AMD 6128 - 2Ghz -
> 2 CPUs
>     (8 Cores/CPU Core - 1GB) 16 Cores Total - 16 GB RAM for AMD-V
> virtualization,
>     and we did the same tests with the same software versions with 2
> nodes of DELL
>     PowerEdge SC1950, biprocessors dual core, 2 Xeon(R) CPU 5160 @
> 3.00GHz,
>     16GB RAM. for Intel VT virtualization. And with Intel technology
> we get the
>     typical virtualization performance, around 2-5% of lost.
> 
>      Thanks in advance,
>         Víctor Fdez.
> 
> El 09/07/13 15:33, Gleb Natapov escribió:
> >On Tue, Jul 09, 2013 at 02:20:43PM +0200, Victor fernandez wrote:
> >>Hi EveryBody!
> >>
> >>recently, we have tested some specific High Energy Physics benchmarks that
> >>was running over S.L.6 and we observed that the performance over AMD
> >>machines was really bad, about 30-40% lost. We were investigating
> >>and we conclude that the problem was with some cpu flags. These cpu
> >>flags are important for running our application because it is optimazed
> >>for running with them. So, we tuning our KVM with the name of flags
> >>parameters and with "-cpu host" parameter too, but
> >>we observed that the flags that we needed, they weren't included when
> >>we started the S.L.6 instance. We try to solve it, but when we conclude
> >>that the specific flags weren't included in the code of the last
> >>versions of KVM
> >>and LibVirt(capabilities). Do you know something about this problem or
> >>you are aware of this?
> >>
> >What flags are missing?
> >
> >--
> >			Gleb.
> 

--
			Gleb.