linux-kernel - Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path

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Date:	Mon, 30 Sep 2013 09:05:51 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Alex Shi <alex.shi@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path


* Michel Lespinasse <walken@...gle.com> wrote:

> That said, I am very scared of using rwlock_t here, and I would much 
> prefer we choose a fair lock (either spinlock or a new rwlock 
> implementation which guarantees not to starve any locker thread)

Given how few users rwlock_t has today we could attempt to make it 
reader-writer fair, as long as the usecase of a hardirq or softirq
context always getting nested read access on the same CPU is preserved. 

(but that can be done - if nothing else then with an explicit context 
check.)

Thanks,

	Ingo
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