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

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Date:	Thu, 09 Jun 2011 05:47:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
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

Le mercredi 08 juin 2011 à 17:05 -0700, David Miller a écrit :
> 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!

Thanks David

I would be glad to hear about numbers from Andi and Tim, I am very
jealous of their 80 Threads machine ;)



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