linux-kernel - Re: [PATCH V16 00/11] x86: Intel Cache Allocation Technology Support

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Message-ID: <20151218204915.GA30427@amt.cnet>
Date:	Fri, 18 Dec 2015 18:49:15 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>,
	Ravi V Shankar <ravi.v.shankar@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH V16 00/11] x86: Intel Cache Allocation Technology Support

On Fri, Dec 18, 2015 at 11:45:29AM -0600, Christoph Lameter wrote:
> On Thu, 17 Dec 2015, Fenghua Yu wrote:
> 
> > 	Intel Cache allocation support:
> >
> > 	Cache allocation patches adds a cgroup subsystem to support the new
> > Cache Allocation feature found in future Intel Xeon Intel processors.
> > Cache Allocation is a sub-feature with in Resource Director
> > Technology(RDT) feature. Current patches support only L3 cache
> > allocation.
> >
> > Cache Allocation provides a way for the Software (OS/VMM) to restrict
> > cache allocation to a defined 'subset' of cache which may be overlapping
> > with other 'subsets'.  This feature is used when a thread is allocating
> > a cache line ie when pulling new data into the cache.
> >
> > Threads are associated with a CLOS(Class of service). OS specifies the
> > CLOS of a thread by writing the IA32_PQR_ASSOC MSR during context
> > switch. The cache capacity associated with CLOS 'n' is specified by
> > writing to the IA32_L3_MASK_n MSR.
> 
> Could you also support another low level interface where a task (or
> process) can set the CLOS id itself if it has CAP_SYS_NICE.

Hi Christoph,

Do you have a proposal for an interface?

>  Plus some way
> for the supervisor to directly control the IA32_L3_MASK_n MSR?

What you mean supervisor? Hypervisor or root user?

> Is there a way to see these values for debugging purposes?

Yes, from userspace, wrmsr and rdmsr.

> We tightly control processes and bind them to processors. cpusets are
> often a too high level instrument at that level.


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