netdev - Re: [PATCH net-next-2.6] inetpeer: do not use zero refcnt for freed entries

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Message-ID: <1276678609.2632.13.camel@edumazet-laptop>
Date:	Wed, 16 Jun 2010 10:56:49 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH net-next-2.6] inetpeer: do not use zero refcnt for
 freed entries

Le mardi 15 juin 2010 à 21:47 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 16 Jun 2010 04:45:24 +0200
> 
> > [PATCH net-next-2.6] inetpeer: do not use zero refcnt for freed entries
> > 
> > Followup of commit aa1039e73cc2 (inetpeer: RCU conversion)
> > 
> > Unused inet_peer entries have a null refcnt.
> > 
> > Using atomic_inc_not_zero() in rcu lookups is not going to work for
> > them, and slow path is taken.
> > 
> > Fix this using -1 marker instead of 0 for deleted entries.
> > 
> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> 
> Applied, thanks Eric.

Thanks

With 65537 peers and a DDOS frag attack, I now get following profiling
results :

-----------------------------------------------------------------------------------------
   PerfTop:    1024 irqs/sec  kernel:100.0%  exact:  0.0% [1000Hz
cycles],  (all, cpu: 0)
-----------------------------------------------------------------------------------------

             samples  pcnt function                  DSO
             _______ _____ _________________________ 

             7722.00 65.6% inet_frag_find            
             1355.00 11.5% ip4_frag_match            
              494.00  4.2% __lock_acquire            
              260.00  2.2% inet_getpeer              
              243.00  2.1% ip_route_input_common     
              151.00  1.3% lock_release              
              142.00  1.2% mark_lock                 
              126.00  1.1% lock_acquire              
              104.00  0.9% __kmalloc                 
               86.00  0.7% skb_put                   


Just to show what could be the next steps ;)





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