linux-kernel - Re: [RFC][PATCH RT] rwsem_rt: Another (more sane) approach to mulit reader rt locks

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Date:	Tue, 22 May 2012 19:07:46 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Clark Williams <williams@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][PATCH RT] rwsem_rt: Another (more sane) approach to mulit
 reader rt locks

On Tue, 22 May 2012, Steven Rostedt wrote:

> On Tue, 2012-05-22 at 18:40 +0200, Thomas Gleixner wrote:
> 
> > > I'm all for benchmarks. But right now, making all readers pass through a
> > > single mutex is a huge bottle neck for a lot of loads. Yes, they are
> > > mostly Java loads, but for some strange reason, our customers seems to
> > > like to run Java on our RT kernel :-p
> > 
> > I'm well aware that mmap_sem is a PITA but replacing one nightmare
> > with the next one is not the best approach.
> 
> Perhaps we could just change the mmap_sem to use this approach. Create a
> new type of rwsem/lock for -rt that we can be picky about.
> 
> Yeah, mmap_sem is a real PITA and it would be nice to have a solution
> that can be used until we can convert it to an RCU lock.

That still wants to be verified with numbers on a machine with at
least 32 cores and workloads which are mmap heavy. And before we don't
have such numbers we can really stop arguing about that solution.

Thanks,

	tglx
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