linux-kernel - Re: [PATCH 0/2] convert mmap_sem to a scalable rw

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Date:	Sat, 12 May 2007 12:01:43 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Esben Nielsen <nielsen.esben@...glemail.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex

On Sat, 2007-05-12 at 11:27 +0200, Esben Nielsen wrote:
> 
> On Fri, 11 May 2007, Peter Zijlstra wrote:
> 
> >
> > I was toying with a scalable rw_mutex and found that it gives ~10% reduction in
> > system time on ebizzy runs (without the MADV_FREE patch).
> >
> 
> You break priority enheritance on user space futexes! :-(
> The problems is that the futex waiter have to take the mmap_sem. And as 
> your rw_mutex isn't PI enabled you get priority inversions :-(

Do note that rwsems have no PI either.
PI is not a concern for mainline - yet, I do have ideas here though.


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