netdev - Re: Kernel rwlock design, Multicore and IGMP

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Message-ID: <1289688826.2109.400.camel@laptop>
Date:	Sat, 13 Nov 2010 23:53:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Cypher Wu <cypher.w@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: Kernel rwlock design, Multicore and IGMP

On Fri, 2010-11-12 at 11:32 +0800, Cypher Wu wrote:
> It seems not a problem that read_lock() can be nested or not since
> rwlock doesn't have 'owner', 

You're mistaken.

> it's just that should we give
> write_lock() a priority than read_lock() since if there have a lot
> read_lock()s then they'll starve write_lock().

We rely on that behaviour. FWIW write preference locks will starve
readers.

> We should work out a well defined behavior so all the
> platform-dependent raw_rwlock has to design under that principle. 

We have that, all archs have read preference rwlock_t, they have to,
code relies on it.
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