Re: [Xen-users] Odd number of VCPU and performance impact?

["Niels Dettenbach (Syndicat IT & Internet)" <nd@xxxxxxxxxxxx>]

Am 17. Januar 2015 08:39:16 MEZ, schrieb mad Engineer 
<themadengin33r@xxxxxxxxx>:
>Thanks Niel,
>                  I have CPU pinning enabled and pinned to proper PCPU
>,but my question is will there be any performance issue if we use odd
>number of VCPU.
This  should be a result of my answer.

I.e. if you  have  two XEON Quad  Core CPUs and want to assign  3 cores  (which 
leads  to a bit less PER core in up to 2 DomUs  compared to  2 or 4 pinned 
cores) you should prefer i.e.  (i  prefer  the second core  here  assuming  
that  one  or two  of the  first  cores  are excusively  bound to  dom0.

1  
2
3
4

5
6 *
7 *
8 *

instead of  i.e.:

1
2
3
4  *

5  *
6  *
7
8

or  if you  want  to  assign 2:

4
5  *
6
7 *

is less  ideal  then:

4
5
6 *
7 *

i.e. intels threaded  cores  are  showing  the double amount of cores  -  each 
two  "cores" are technically a full core  - i.e. for a quad CPU:

1 2
3 4
5 6
7 8

and  even here  you  should prefer to use complete cores (doublettes)  - 
usually counted from 0.


hth a bit.
cheerioh,

Niels.
-- 
Niels Dettenbach
Syndicat IT & Internet
http://www.syndicat.com

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