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

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Message-ID: <4645DCA2.80408@cosmosbay.com>
Date:	Sat, 12 May 2007 17:26:26 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Esben Nielsen <nielsen.esben@...glemail.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, 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

Esben Nielsen a écrit :
> 
> 
> On Sat, 12 May 2007, Peter Zijlstra wrote:
> 
>> 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.
>>
>>
> If PI wasn't a concern for mainline, why is PI futexes merged into the 
> mainline?

If you really care about futexes and mmap_sem, just use private futexes, since 
they dont use mmap_sem at all.


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