Re: [Xen-devel] [PATCH v1 01/13] docs: create Memory Bandwidth Allocation (MBA) feature document

[Yi Sun <yi.y.sun@xxxxxxxxxxxxxxx>]

On 17-08-14 15:35:38, Chao Peng wrote:
> 
> > +     Linear mode: the input precision is defined as 100-(MBA_MAX).
> > For instance,
> > +     if the MBA_MAX value is 90, the input precision is 10%. Values
> > not an even
> > +     multiple of the precision (e.g., 12%) will be rounded down
> > (e.g., to 10%
> > +     delay applied) by HW automatically.
> 
> No sure if all people unterstand HW, if not then I prefer Hardware. If
> you do this then all places though the document should be replaced.
> 
We may explain 'HW' in 'Terminology'.

> 
> > +  When context switch happens, the COS ID of VCPU is written to per-
> > thread MSR
> 
> COS ID is per-domain other than per-vCPU at this time. So 'COS ID of
> domain' is more accurate.
> 
Yes, thanks.

> > +  `IA32_PQR_ASSOC`, and then hardware enforces bandwidth allocation
> > according
> > +  to the throttling value stored in the COS register.
> 
> There is no COS register in fact. COS exists just a concept.
> 
Ok, I will state the formal register name defined in SDM here.

> > +For example:
> > +    root@:~$ xl psr-hwinfo --mba
> > +    Memory Bandwidth Allocation (MBA):
> > +    Socket ID       : 0
> > +    Linear Mode     : Enabled
> > +    Maximum COS     : 7
> > +    Maximum Throttling Value: 90
> > +    Default Throttling Value: 0
> > +
> > +    root@:~$ xl psr-mba-set 1 0xa
> > +
> > +    root@:~$ xl psr-mba-show 1
> > +    Socket ID       : 0
> > +    Default THRTL   : 0
> > +       ID                     NAME            THRTL
> > +        1                 ubuntu14             0xa
> > +
> > +# Areas for improvement
> > +
> > +A hexadecimal number is used to show THRTL for a domain now. It may
> > not be user-
> > +friendly.
> > +
> > +To improve this, the libxl interfaces can be wrapped in libvirt to
> > provide more
> > +usr-friendly interfaces to user, e.g. a percentage number to show for
> > linear
> > +mode.
> 
> I suggest we can do this even for 'xl psr-mba-show', as we know we are
> in linear mode or not. A hex number is just not easy to understand for

So your suggestion is to show decimal value for linear mode, right? How about
non-linear mode, still show hexadecimal value?

> people. And for 'xl psr-mba-set' it is also much straighforward to set a
> percentage number in linear mode.
> 
For set, we do not have any limitation. User can input decimal or hexadecimal
value.

> Chao

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