Re: [Qemu-discuss] Puzzling performance comparison with KVM and Hyper-V

[Stephan von Krawczynski]

On Tue, 21 Jul 2015 15:12:26 +0000
Carlos Torres <address@hidden> wrote:

> 
> ________________________________________
> From: Tim Bell <address@hidden>
> Sent: Tuesday, July 21, 2015 9:53 AM
> To: Stephan von Krawczynski
> Cc: Carlos Torres; address@hidden
> Subject: Re: [Qemu-discuss] Puzzling performance comparison with KVM and 
> Hyper-V
> 
> On Tue, 21 Jul 2015, Stephan von Krawczynski wrote:
> 
> > On Tue, 21 Jul 2015 16:16:22 +0200
> > Tim Bell <address@hidden> wrote:
> >
> >>
> >>
> >> On Tue, 21 Jul 2015, Carlos Torres wrote:
> >>
> >>> On Jul 21, 2015 5:45 AM, Tim Bell <address@hidden> wrote:
> 
> >
> > Have you worked out the pinning? The cpu numbers are _not_ in line with
> > core/SMT distribution over the physical dies.
> >
> 
> I think we did it correctly but please give me some pointers to check...
> the vCPU to CPU mapping we used was as below
> 
> vCPU:CPU
> 0: 0
> 1: 1
> 2: 2
> 3: 3
> 4: 4
> 5: 5
> 6: 6
> 7: 7
> 8: 16
> 9: 17
> 10: 18
> 11: 19
> 12: 20
> 13: 21
> 14: 22
> 15: 23
> 16: 8
> 17: 9
> 18: 10
> 19: 11
> 20: 12
> 21: 13
> 22: 14
> 23: 15
> 24: 24
> 25: 25
> 26: 26
> 27: 27
> 28: 28
> 29: 29
> 30: 30
> 31: 31
> 
> >
> > --
> > Regards,
> > Stephan
> >
> 
> Hi Tim,
> 
> 'cat /proc/cpuinfo' should give you this information, look at the processor, 
> physical id and core id values
> 
> For example, here's an excerpt from my laptop that has 4 physical cores up to 
> 2 threads per core (8 cpus total).
> 
> processor       : 0                         <=== CPU # given by the OS
> vendor_id       : GenuineIntel
> .....
> physical id     : 0                         <==== Physical Processor Socket ID
> siblings        : 8
> core id         : 0                           <==== Physical CPU Core ID
> cpu cores       : 4
> ....
> 
> processor       : 1                      
> vendor_id       : GenuineIntel
> .....
> physical id     : 0                        <=== Same Processor socket (my 
> laptop has only 1)
> siblings        : 8
> core id         : 1                          <==== Distinct CPU Physical core
> cpu cores       : 4
> 
> ....
> 
> processor       : 4                    
> vendor_id       : GenuineIntel
> .....
> physical id     : 0                      <=== Still same Processor socket 
> (expected)
> siblings        : 8
> core id         : 0                        <=== Note this is the same 
> physical core as processor 0 above
> cpu cores       : 4
> 
> 
> -- Carlos Torres

Carlos is right. You have to closely check /proc/cpuinfo, look at this example
from a box with 2 physical processors and 8 cores 2 threads each (32 overall):

processor       : 0
physical id     : 0
siblings        : 16
core id         : 0
cpu cores       : 8

processor       : 1
physical id     : 1
siblings        : 16
core id         : 0
cpu cores       : 8

processor       : 2
physical id     : 0
siblings        : 16
core id         : 1
cpu cores       : 8

processor       : 3
physical id     : 1
siblings        : 16
core id         : 1
cpu cores       : 8

...

As you can see processor 0 and 2 are on physical id 0 but processor 1 and 3
are on physical id _1_. This means that 0 and 1 are on a completely different
die inside the box which has heavy impact on numa setup and access.
There is no hint anyone can give you, you have to check your very personal
setup here to find out what logical processor is located where.
You have to arrange the pinning so that multiple processors in one virtual
host are located as near as possible. Stay on the same die and if possible use
the SMT as nearest neighbor because it has the same cache.

-- 
Regards,
Stephan