Re: Question about the CAT and CMT in Xen

[Chao Peng <chao.p.peng@linux.intel.com>]

On Tue, Sep 01, 2015 at 10:42:57AM -0400, Meng Xu wrote:
> 2015-09-01 10:30 GMT-04:00 Andrew Cooper <andrew.cooper3@citrix.com>:
> > On 01/09/15 15:20, Meng Xu wrote:
> >> 2015-09-01 9:04 GMT-04:00 Andrew Cooper <andrew.cooper3@citrix.com>:
> >>> On 01/09/15 13:55, Meng Xu wrote:
> >>>> 2015-09-01 1:47 GMT-04:00 Chao Peng <chao.p.peng@linux.intel.com>:
> >>>>> On Mon, Aug 31, 2015 at 04:09:31PM -0400, Meng Xu wrote:
> >>>>>> I looked into the xen/arch/x86/psr.c and found that the function
> >>>>>> cat_cpu_init() just returned without initializing the variable
> >>>>>> "cat_socket_enable".
> >>>>>>
> >>>>>> Both  !cpu_has(c, X86_FEATURE_CAT) and c->cpuid_level <
> >>>>>> PSR_CPUID_LEVEL_CAT are evaluated as 1 inside the function
> >>>>>> cat_cpu_init().
> >>>>>>
> >>>>>> OK. I understand that  the cpuid info shows that the CPU does not
> >>>>>> support CAT. However, according to the table at
> >>>>>> http://www.intel.com/content/www/us/en/communications/cache-monitoring-cache-allocation-technologies.html,
> >>>>>>  Intel(R) Xeon(R) CPU E5-2618L v3 should support CAT.
> >>>>>>
> >>>>>> I'm not sure which part is incorrect: the hardware or the software?
> >>>>>> (Hope Chao could give some insight about this.)
> >>>>>>
> >>>>> Hmmm, from cpuid info it looks like this model does not support CAT. I'm
> >>>>> not sure which microarchitecture it is.
> >>>> According to http://www.cpu-world.com/CPUs/Xeon/Intel-Xeon%20E5-2618L%20v3.html,
> >>>> 2618L v3 is Haswell. :-(
> >>> Wikipedia agrees.
> >>>
> >>> Haswell only has plain L3 cache usage information.
> >>>
> >>> It is Broadwell which adds memory bandwidth monitoring, and Cache
> >>> Allocation.
> >> Ah, then the Intel's website [1] that lists the CAT-enabled processor
> >> is quite misleading. I checked several processors (2618Lv3, 2608Lv3,
> >> 2658v3) listed  in [1] that is claimed to have CAT, and all of them
> >> belong to Haswell... I think "v3" actually represents Haswell.
> >>
> >> Andrew, is it possible to know which processor XenServer is currently
> >> using that is confirmed to have the CAT mechanism?
> >
> > I cant be much help, unfortunately,
> 
> Thank you very much for your trying to help! :-)
> 
> Hope Chao could give more information about which Intel processors
> support the CAT.

Until now what I can tell you is: All Broadwell Server support CAT and some
models of Haswell Server may also support it.

And the good news is the information @ Intel's website [1] is accurate
so your purchased "E5-2618L v3" should have it. But you definitely need
to ask your vendor for the firmware update.

Chao