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Date: Wed, 14 Sep 2016 18:13:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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Subject: Re: [PATCH] android: binder: Disable preemption while holding the
 global binder lock
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On Wed, Sep 14, 2016 at 06:11:03PM +0200, Peter Zijlstra wrote:
> 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.

Not to mention the fact that the weight depends on the current running
state. Having those tasks block insta changes the actual weight.

> /me curses @ cgroups.. bloody stupid things.

More of that.