linux-kernel - Re: [PATCH 3/7] x86/intel_rdt: Support cache bit mask for Intel CAT

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Date:	Wed, 6 May 2015 09:48:41 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vikas Shivappa <vikas.shivappa@...el.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...nel.org, tj@...nel.org,
	Matt Fleming <matt.fleming@...el.com>,
	"Auld, Will" <will.auld@...el.com>, peter.zijlstra@...el.com,
	h.peter.anvin@...el.com,
	"Juvva, Kanaka D" <kanaka.d.juvva@...el.com>
Subject: Re: [PATCH 3/7] x86/intel_rdt: Support cache bit mask for Intel
 CAT



On Wed, 6 May 2015, Peter Zijlstra wrote:

> On Mon, May 04, 2015 at 10:30:15AM -0700, Vikas Shivappa wrote:
>> On Sat, 2 May 2015, Peter Zijlstra wrote:
>>
>>>
>>> There's CAT in your subject, make up your minds already on what you want
>>> to call this stuff.
>>
>> We dont have control over the names.It is clear from the patch 0/7 where its
>
> If I read 0/n its _after_ I've read all the other patches. The thing is,
> 0/n should not contain anything persistent. Patches should stand on
> their own.
>
>> explained that RDT is the umbrella term and CAT is a part of it and this
>> patch series is only for CAT ... It also mentions what exact section of the
>> Intel manual this refers to. Is there still some lack of clarification here
>> ?
>
> But we're not implementing an umbrella right? We're implementing Cache
> QoS Enforcement (CQE aka. CAT).

In some sense we are - The idea was that the same rdt cgroup would include other 
features in the rdt and 
cache allocation is one of them. Hence the cgroup name is RDT. Like Matt just 
commented we just found some naming issues with respect to the APIs whether to 
use cat or rdt. I can plan to remove the 'cat' altogether and use cache alloc 
as I just learnt it may be not liked because its cat(mean an animal.. in english 
:) )

Only reason to do it now is that we cant change the cgroup name later.

>
> Why confuse things with calling it random other names?
>
> From what I understand the whole RDT thing is the umbrella term for
> Cache QoS Monitoring and Enforcement together. CQM is implemented
> elsewhere, this part is only implementing CQE.
>
> So just call it that, calling it RDT is actively misleading, because it
> explicitly does _NOT_ do the monitoring half of it.
>
>> If its just your disliking the term thats already known.
>
> I think its crazy to go CQE no CAT no RDT, but I could get over that in
> time. But now it turns out you need _both_, and that's even more silly.

I agree the changing of names have led to enough confusion and we can try to see 
that if we can make this better in coming features.
I will send fixes where I will try to be more clear on names. 
Basically have rdt for things which would be common to cache alloc and all other 
features and keep cache alloc which is specific to cache alloc (like the 
cache bit mask is only for cache alloc)..

>
>
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