netdev - Re: neighbour table RCU

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Date:	Tue, 1 Sep 2009 09:23:17 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Octavian Purdila <opurdila@...acom.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Lucian Adrian Grijincu <lgrijincu@...acom.com>,
	netdev@...r.kernel.org
Subject: Re: neighbour table RCU

On Tue, 1 Sep 2009 18:55:34 +0300
Octavian Purdila <opurdila@...acom.com> wrote:

> On Tuesday 01 September 2009 09:50:17 Eric Dumazet wrote:
> > 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.
> >
> 
> Speaking about neighbour optimizations, here is a RFC patch which makes the 
> tables double linked, for constant time deletion. It has given us a significant 
> performance improvement - in less then usual setups though, with lots of 
> neighbours.
> 
> Would something like this be acceptable for upstream? (pardon the p4 diff dump 
> :) - but I think it will give a rough idea, if acceptable will clean it up and 
> properly submit it)
> 
> BTW, would switching to list_head be better?

Use hlist for the neighbour table. It has the right properties
and makes future RCU easier.
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