netdev - Re: [PATCH net-next-2.6] inetpeer: remove unused list

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Message-Id: <20110608.170557.2273990802892743973.davem@davemloft.net>
Date:	Wed, 08 Jun 2011 17:05:57 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	tim.c.chen@...ux.intel.com, andi@...stfloor.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] inetpeer: remove unused list

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 09 Jun 2011 01:35:34 +0200

> Andi Kleen and Tim Chen reported huge contention on inetpeer
> unused_peers.lock, on memcached workload on a 40 core machine, with
> disabled route cache.
> 
> It appears we constantly flip peers refcnt between 0 and 1 values, and
> we must insert/remove peers from unused_peers.list, holding a contended
> spinlock.
> 
> Remove this list completely and perform a garbage collection on-the-fly,
> at lookup time, using the expired nodes we met during the tree
> traversal.
> 
> This removes a lot of code, makes locking more standard, and obsoletes
> two sysctls (inet_peer_gc_mintime and inet_peer_gc_maxtime). This also
> removes two pointers in inet_peer structure.
> 
> There is still a false sharing effect because refcnt is in first cache
> line of object [were the links and keys used by lookups are located], we
> might move it at the end of inet_peer structure to let this first cache
> line mostly read by cpus.
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Didn't expect you to implement this so fast :-)

Applied, thanks!
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