Re: [Xen-devel] [PATCH v3 01/15] docs: create Memory Bandwidth Allocation (MBA) feature document

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Roger Pau Monné <roger.pau@xxxxxxxxxx> 09/18/17 7:21 PM >>>
>On Tue, Sep 05, 2017 at 05:32:23PM +0800, Yi Sun wrote:
>> +## Hardware perspective
>> +
>> +  MBA defines a range of MSRs to support specifying a delay value (Thrtl) 
>> per
>> +  COS, with details below.
>> +
>> +  ```
>> +   +----------------------------+----------------+
>> +   | MSR (per socket)           |    Address     |
>> +   +----------------------------+----------------+
>> +   | IA32_L2_QOS_Ext_BW_Thrtl_0 |     0xD50      |
>> +   +----------------------------+----------------+
>> +   | ...                        |  ...           |
>> +   +----------------------------+----------------+
>> +   | IA32_L2_QOS_Ext_BW_Thrtl_n |     0xD50+n    |
>> +   +----------------------------+----------------+
>> +  ```
>> +
>> +  When context switch happens, the COS ID of domain is written to 
>> per-thread MSR
>> +  `IA32_PQR_ASSOC`, and then hardware enforces bandwidth allocation 
>> according
>
>I think this is missing some context of the relation between a thread
>and the MSR. I assume it's related to IA32_PQR_ASSOC, but I have no
>idea what that constant means.
>
>What's more, Xen doesn't have threads, so you should maybe speak about
>vCPUs instead?

I think talk is of hardware aspects here, i.e. "thread" as in "hyper-thread".

Jan


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