Re: Question about the CAT and CMT in Xen

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Meng Xu <xumengpanda@gmail.com>
Cc: Chao Peng <chao.p.peng@linux.intel.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: Question about the CAT and CMT in Xen
Date: Tue, 1 Sep 2015 15:30:13 +0100	[thread overview]
Message-ID: <55E5B675.7020607@citrix.com> (raw)
In-Reply-To: <CAENZ-+kiiGQV_MLL-5Xr-xsRcu9YYqWBNqTUJv_z9Fr20er06A@mail.gmail.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,

>From /proc/cpuinfo
processor    : 14
vendor_id    : GenuineIntel
cpu family    : 6
model        : 79
model name    : Genuine Intel(R) CPU 0000 @ 2.20GHz

This is a 2-socket Broadwell-EP SDP and is probably a firmware revision
out of date, but I can confirm that I have had a bit of a play with CMT
and CAT on it.

~Andrew