linux-kernel - Re: [patch RT 0/4] rwsem/rt: Lift the single reader restriction

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Date:   Tue, 4 Apr 2017 16:01:02 +0200
From:   Sebastian Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        RT-users <linux-rt-users@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>, Wargreen <wargreen@...ib.org>
Subject: Re: [patch RT 0/4] rwsem/rt: Lift the single reader restriction

On 2017-04-01 12:50:58 [+0200], Thomas Gleixner wrote:
> R/W semaphores in RT do not allow multiple readers because a writer
> blocking on the sempahore would have deal with all the readers in terms of
> priority or budget inheritance. While multi reader priority boosting would
> be possible (it has been attempted before), multi reader budget inheritance
> is impossible.
…
> It cures the Radeon mess, lowers the contention on mmap_sem for certain
> workloads and did not have any negative impact in our initial testing on RT
> behaviour.
> 
> I think it's worth to expose it to a wider audience of users for testing,
> so we can figure out it whether there are dragons lurking.

series applied.

> Thanks,
> 
> 	tglx

Sebastian