netdev - Re: [PATCH net-next-2.6] net: sk_dst

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Date:	Tue, 13 Apr 2010 01:52:32 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH net-next-2.6] net: sk_dst_cache RCUification

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 09 Apr 2010 11:03:29 +0200

> With latest CONFIG_PROVE_RCU stuff, I felt more comfortable to make this
> work.
> 
> sk->sk_dst_cache is currently protected by a rwlock (sk_dst_lock)
> 
> This rwlock is readlocked for a very small amount of time, and dst
> entries are already freed after RCU grace period. This calls for RCU
> again :)
> 
> This patch converts sk_dst_lock to a spinlock, and use RCU for readers.
> 
> __sk_dst_get() is supposed to be called with rcu_read_lock() or if
> socket locked by user, so use appropriate rcu_dereference_check()
> condition (rcu_read_lock_held() || sock_owned_by_user(sk))
> 
> This patch avoids two atomic ops per tx packet on UDP connected sockets,
> for example, and permits sk_dst_lock to be much less dirtied.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, thanks for doing this work Eric.
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