linux-kernel - RE: [PATCH 3/9] x86/intel_rdt: Cache Allocation documentation and cgroup usage guide

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Date:	Wed, 29 Jul 2015 13:07:30 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	"Auld, Will" <will.auld@...el.com>
cc:	"Shivappa, Vikas" <vikas.shivappa@...el.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"tj@...nel.org" <tj@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"Fleming, Matt" <matt.fleming@...el.com>,
	"Williamson, Glenn P" <glenn.p.williamson@...el.com>,
	"Juvva, Kanaka D" <kanaka.d.juvva@...el.com>
Subject: RE: [PATCH 3/9] x86/intel_rdt: Cache Allocation documentation and
 cgroup usage guide



On Tue, 28 Jul 2015, Auld, Will wrote:

>
>
>> -----Original Message-----
>>
>> Same comment as above - Cgroup masks can always overlap and other cgroups
>> can allocate the same cache , and hence wont have exclusive cache allocation.
>
> [Auld, Will] You can define all the cbm to provide one clos with an exclusive area

Do you mean a CLOS that has all the bits set. We donot support exclusive area 
today. The bits in the mask can overlap .. hence can always share the same cache 
allocation .

>
>>
>> So natuarally the cgroup with tasks would get to use the cache if it has the same
>> mask (say representing 50% of cache in your example) as others .
>
> [Auld, Will] automatic adjustment of the cbm make me nervous. There are times
> when we want to limit the cache for a process independent of whether there is
> lots of unused cache.
>

Please see example below - In general , I just mean the cache mask can have bits 
that can overlap - does not matter whether there is tasks in it or not.

>
>> (assume there are 8 bits max cbm)
>> cgroupa - mask - 0xf
>> cgroupb - mask - 0xf . Now if cgroupa has no tasks , cgroupb naturally gets all
>> the cache.
>>
>> Thanks,
>> Vikas
--
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