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Re: [Xen-devel] [RFC Design Doc] Intel L2 Cache Allocation Technology (L2 CAT) Feature enabling

On Thu, May 12, 2016 at 04:05:36AM -0600, Jan Beulich wrote:
> >>> On 12.05.16 at 11:40, <he.chen@xxxxxxxxxxxxxxx> wrote:
> > % Intel L2 Cache Allocation Technology (L2 CAT) Feature
> > % Revision 1.0
> > 
> > \clearpage
> > 
> > Hi all,
> > 
> > We plan to bring new PQoS feature called Intel L2 Cache Allocation
> > Technology (L2 CAT) to Xen.
> > 
> > L2 CAT is supported on Atom codename Goldmont and beyond. “Big-core”
> > Xeon does not support L2 CAT in current generations.
> Looks mostly like a direct (and hence reasonable) extension of what
> we have for L3 right now. One immediate question I have is whether
> tying this to per-socket information is a good idea. As soon as Xeon-s
> would also gain such functionality, things would (aiui) need to become
> per-core (as L2 is per core there iirc).

L2 Cache capability keeps the same through all cores in a socket, so we
make it per-socket to balance code complexity and accessibility.

I am not a expert in scheduler, do you mean in some cases, a domain
would apply different L2 cache access pattern when it is scheduled on
different cores even though the cores are in the same socket?

> The other question is whether with Xen we care enough about Atoms
> to add code that's of use only there.

L2 CAT is a platform independent feature although it firstly shows in
Atoms and I believe that it will appear in other platform soon.


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