netdev - Re: neighbour table RCU

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Message-ID: <4A9CC429.5020803@gmail.com>
Date:	Tue, 01 Sep 2009 08:50:17 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	netdev@...r.kernel.org
Subject: Re: neighbour table RCU

Stephen Hemminger a écrit :
> Looking at the neighbour table, it should be possible to get
> rid of the two reader/writer locks.  The hash table lock is pretty
> amenable to RCU, but the dynamic resizing makes it non-trivial.
> Thinking of using a combination of RCU and sequence counts so that the
> reader would just rescan if resize was in progress.

I am not sure neigh_tbl_lock rwlock should be changed, I did not
see any contention on it.

> 
> The reader/writer lock on the neighbour entry is more of a problem.
> Probably would be simpler/faster to change it into a spinlock and
> be done with it.
> 
> The reader/writer lock is also used for the proxy list hash table,
> but that can just be a simple spinlock.
> 

This is probably is the only thing we want to do at this moment,
halving atomic ops on neigh_resolve_output()

But why neigh_resolve_output() was called so much in the bench
is the question...

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