linux-kernel - Re: [PATCH V15 00/11] x86: Intel Cache Allocation Technology Support

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Date:	Mon, 19 Oct 2015 21:49:10 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Subject: Re: [PATCH V15 00/11] x86: Intel Cache Allocation Technology Support

On Fri, Oct 16, 2015 at 05:24:42PM -0300, Marcelo Tosatti wrote:
> On Fri, Oct 16, 2015 at 11:44:52AM +0200, Peter Zijlstra wrote:
> > On Thu, Oct 15, 2015 at 09:17:16PM -0300, Marcelo Tosatti wrote:
> > > On Thu, Oct 15, 2015 at 01:37:02PM +0200, Peter Zijlstra wrote:
> > > > On Tue, Oct 13, 2015 at 07:40:58PM -0300, Marcelo Tosatti wrote:
> > > > > How can you fix the issue of sockets with different reserved cache
> > > > > regions with hw in the cgroup interface?
> > > > 
> > > > No idea what you're referring to. But IOCTLs blow.
> > > 
> > > Tejun brought up syscalls. Syscalls seem too generic.
> > > So ioctls were chosen instead.
> > > 
> > > It is necessary to perform the following operations:
> > > 
> > > 1) create cache reservation (params = size, type).
> > 
> > mkdir

You need to specify type and size. So could be:

cd ../cgroups/intel_cat_cgroup/
mkdir reservation-a
cd reservation-a
echo 1000 > size
echo code > type
echo $pid > tasks

So each directory in the intel cat cgroup specifies a reservation, which
contains:
	* size.
	* type.
	* tasks which the reservation is attached to.

> > > 2) delete cache reservation.
> > 
> > rmdir

Detach would simply work when removing tasks from "tasks" field.

> > > 3) attach cache reservation (params = cache reservation id, pid).
> > > 4) detach cache reservation (params = cache reservation id, pid).
> > 
> > echo $pid > tasks
> > 
> > > Can it done via cgroups? If so, works for me.
> > 
> > Trivially.
> 
> Fine. 
> 
> Tejun brought the problem of locking: how do you coordinate locking
> between different users?  (on the mkdir / rmdir scenario above).

Can't see locking issue with "reservation" based interface (that is each
directory is a cache reservation).

Tejun, any comments on this non hierarchical cgroup interface?

(still waiting on you to reply the other emails on this thread, Peter).

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