Re: [Xen-devel] [PATCH v10 09/25] x86: refactor psr: L3 CAT: set value: implement framework.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.04.17 at 08:40, <yi.y.sun@xxxxxxxxxxxxxxx> wrote:
> As what we talked on IRC last Friday, I have got answers for your
> two final questions below:
> 1. Why domain setting is designed to per-socket, any reason? 
> Answer: There is a real case from Intel's customer. HSX (Haswell server)
> and BDX (Broadwell server) processors are plugged into each socket of a
> Grantley platform. HSX does not support CAT but BDX does.
> 
> You and Chao Peng discussed this before for CAT feature enabling patches.
> The asymmetry supporting is agreed.

I don't see any agreement in those threads. The first sub-thread is
merely mentioning this configuration, while the second is only about
nr_sockets calculation.

> http://markmail.org/message/xcq5odezfngszvcb#query:+page:1+mid:smfz7fbatbnxs 
> 3ti+state:results
> http://markmail.org/message/xcq5odezfngszvcb#query:+page:1+mid:wlovqpg7oj63e 
> jte+state:results
> 
> 2. Why cannot the previous setting to the domains be kept when socket is 
> online?
> Answer: If the asymmetry system is supported, we cannot assume the 
> configuration
> can be applied to new socket.

I'm afraid we'd have problems elsewhere if we tried to run Xen on
a mixed-model system. Unless you can prove PSR/CAT is the only
relevant (read: affecting Xen's behavior) hardware difference
between Haswell and Broadwell (for example, isn't the former
SMEP only, but the latter SMEP+SMAP?), I don't buy this as a
reason to have more complicated than necessary code.

Jan


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