Re: [PATCH RFC] ioctl based CAT interface

From: Peter Zijlstra <peterz@infradead.org>
To: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vikas Shivappa <vikas.shivappa@intel.com>,
	Tejun Heo <tj@kernel.org>, Yu Fenghua <fenghua.yu@intel.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] ioctl based CAT interface
Date: Mon, 16 Nov 2015 17:26:57 +0100	[thread overview]
Message-ID: <20151116162657.GX17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20151116111842.0c0a30f9@redhat.com>

On Mon, Nov 16, 2015 at 11:18:42AM -0500, Luiz Capitulino wrote:
> Peter, I'm giving a serious try on the cgroups patches and would be
> glad to be enlightened if I'm missing something. But I don't see how
> what you're proposing would solve the problem.
> 
> My understanding of CAT is that if I want to reserve 80% of the cache
> in socket-1 to $thread-A I also have to:
> 
>  1. Create another mask reserving 20% of the cache in socket-1
>  2. Assign that mask to all other threads that may run in socket-1
> 
> If I'm right about this, then when a task with 20% reservation migrates
> to socket-2 it will only access 20% of the cache there even though there
> should be no restrictions in socket-2's cache.

Uh what? Task-A was bound to socket-1, it will never get to socket-2.

Clearly I'm not getting these examples you're throwing around.

Also, I explicitly do not want tasks that can migrate between sockets to
have different performance profiles across those sockets.