linux-kernel - Re: [PATCH V16 11/11] x86,cgroup/intel_rdt : Add a cgroup interface to manage Intel cache allocation

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Message-ID: <alpine.DEB.2.11.1512191139490.28591@nanos>
Date:	Sat, 19 Dec 2015 11:42:57 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Fenghua Yu <fenghua.yu@...el.com>
cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
	Ravi V Shankar <ravi.v.shankar@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Subject: Re: [PATCH V16 11/11] x86,cgroup/intel_rdt : Add a cgroup interface
 to manage Intel cache allocation

On Thu, 17 Dec 2015, Fenghua Yu wrote:

> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> From: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
> 
> Add a new cgroup 'intel_rdt' to manage cache allocation. Each cgroup
> directory is associated with a class of service id(closid). To map a
> task with closid during scheduling, this patch removes the closid field
> from task_struct and uses the already existing 'cgroups' field in
> task_struct.
> 
> The cgroup has a file 'l3_cbm' which represents the L3 cache capacity
> bitmask(CBM). The CBM is global for the whole system currently. The
> capacity bitmask needs to have only contiguous bits set and number of
> bits that can be set is less than the max bits that can be set. The
> tasks belonging to a cgroup get to fill in the L3 cache represented by
> the capacity bitmask of the cgroup. For ex: if the max bits in the CBM
> is 10 and the cache size is 10MB, each bit represents 1MB of cache
> capacity.
> 
> Root cgroup always has all the bits set in the l3_cbm. User can create
> more cgroups with mkdir syscall. By default the child cgroups inherit
> the capacity bitmask(CBM) from parent. User can change the CBM specified
> in hex for each cgroup. Each unique bitmask is associated with a class
> of service ID and an -ENOSPC is returned once we run out of
> closids.

This is still the original crap. No, we are not introducing this
interface now just because we can. I explained in great length why
this is completely useless and what we really need.

Thanks,

	tglx


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