From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1763870AbcINQLM (ORCPT <rfc822;w@1wt.eu>);
        Wed, 14 Sep 2016 12:11:12 -0400
Received: from bombadil.infradead.org ([198.137.202.9]:49133 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1756775AbcINQLL (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 14 Sep 2016 12:11:11 -0400
Date: Wed, 14 Sep 2016 18:11:03 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
        Riley Andrews <riandrews@android.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>, Todd Kjos <tkjos@google.com>
Subject: Re: [PATCH] android: binder: Disable preemption while holding the
 global binder lock
Message-ID: <20160914161103.GC5016@twins.programming.kicks-ass.net>
References: <CAHRSSEwkj-VxstqCm6JzVQcmZzxLQcob0JNiEhzes9oT0-tXSg@mail.gmail.com>
 <20160910161659.GA7987@infradead.org>
 <20160910162210.GK10153@twins.programming.kicks-ass.net>
 <alpine.DEB.2.20.1609101835360.5560@nanos>
 <20160910172843.GA17876@kroah.com>
 <CAMP5XgfDybsfz-v2NTYqAX8K48xCJ_zkH65AHosAOmT7P=Gyxg@mail.gmail.com>
 <20160913073259.GC5008@twins.programming.kicks-ass.net>
 <CAMP5Xgc89ZONamzB4gmnH3RjW5rDSwh3Akrx30npfTiZ1qGzWg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CAMP5Xgc89ZONamzB4gmnH3RjW5rDSwh3Akrx30npfTiZ1qGzWg@mail.gmail.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Sep 13, 2016 at 12:53:27PM -0700, Arve Hjønnevåg wrote:
> On Tue, Sep 13, 2016 at 12:32 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > cgroups should be irrelevant, PI is unaware of them.
> 
> I don't think cgroups are irrelevant. PI being unaware of them
> explains the problem I described. If the task that holds the lock is
> in a cgroup that has a low cpu.shares value, then boosting the task's
> priority within that group does necessarily make it any more likely to
> run.

Thing is, for FIFO/DL the important parameters (prio and deadline resp.)
are not cgroup dependent.

For CFS you're right, and as per usual, cgroups will be a royal pain.
While we can compute the total weight in the block chain, getting that
back to a task which is stuck in a cgroup is just not going to work
well.

The only 'solution' I can come up with in a hurry is, when the task is
boosted, move it to the root cgroup. That of course has a whole heap of
problems all on its own.

/me curses @ cgroups.. bloody stupid things.