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

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Date:	Sat, 12 May 2007 11:27:13 +0200 (CEST)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 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 :-(

Esben
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