linux-kernel - Re: [PATCH] android: binder: Disable preemption while holding the global binder lock

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Message-ID: <20160914133826.GD5020@twins.programming.kicks-ass.net>
Date:   Wed, 14 Sep 2016 15:38:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arve Hjønnevåg <arve@...roid.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        Riley Andrews <riandrews@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH] android: binder: Disable preemption while holding the
 global binder lock

On Wed, Sep 14, 2016 at 09:10:01AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 13, 2016 at 12:53:27PM -0700, Arve Hjønnevåg wrote:

> > Most of the tasks here are not RR/FIFO/DL tasks. I don't see anything
> > in the rtmutex code or documentation that indicates that they don't
> > work for normal tasks. From what I can tell the priority gets boosted
> > in every case. This may not work as well for CFS tasks as for realtime
> > tasks, but it should at least help when there is a large priority
> > difference.
> 
> It does something (it used to explicitly ignore OTHER) but its not
> something well defined or usable.

I looked again, and while it updates the ->prio field for OTHER tasks,
that does not seem to cause a change to the actual weight field (which
is derived from ->static_prio).

So it really should not do anything.. as I remebered it.