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From: Eric Dumazet <eric.dumazet@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: therbert@google.com, alexander.h.duyck@intel.com, netdev@vger.kernel.org
Subject: Re: Performance regression on kernels 3.10 and newer
Date: Sat, 06 Sep 2014 08:46:24 -0700	[thread overview]
Message-ID: <1410018384.11872.33.camel@edumazet-glaptop2.roam.corp.google.com> (raw)
In-Reply-To: <1410017237.11872.31.camel@edumazet-glaptop2.roam.corp.google.com>

On Sat, 2014-09-06 at 08:27 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Alexander Duyck reported high false sharing on dst refcount in tcp stack
> when prequeue is used. prequeue is the mechanism used when a thread is
> blocked in recvmsg()/read() on the TCP socket.
> 
> We already try to use RCU in input path as much as possible, but we were
> forced to take a refcount on the dst when skb escaped RCU protected
> region. When/if the user thread runs on different cpu, dst_release()
> will then touch dst refcount again.
> 
> Commit 093162553c33 (tcp: force a dst refcount when prequeue packet)
> was an example of a race fix.
> 
> It turns out the only remaining usage of skb->dst for a packet stored
> in a TCP socket prequeue is IP early demux.
> 
> We can add a logic to detect when IP early demux is probably going
> to use skb->dst.
> 
> In IPv4 stack, we also can drop dst when skb has to be queued into
> socket backlog. IPv6 needs extra care before doing the same.
> 
> Many thanks to Alexander for providing a nice bug report, git bisection,
> and reproducer.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: Alexander Duyck <alexander.h.duyck@intel.com>

Works fine on IPv4, not on IPv6, I will submit a v2 (with a proper title
btw)

  reply	other threads:[~2014-09-06 15:46 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-14 18:19 Performance regression on kernels 3.10 and newer Alexander Duyck
2014-08-14 18:46 ` Eric Dumazet
2014-08-14 19:50   ` Eric Dumazet
2014-08-14 19:59   ` Rick Jones
2014-08-14 20:31     ` Alexander Duyck
2014-08-14 20:51       ` Eric Dumazet
2014-08-14 20:46     ` Eric Dumazet
2014-08-14 23:16   ` Alexander Duyck
2014-08-14 23:20     ` David Miller
2014-08-14 23:25       ` Tom Herbert
2014-08-21 23:24         ` David Miller
2014-09-06 14:45           ` Eric Dumazet
2014-09-06 15:27             ` Eric Dumazet
2014-09-06 15:46               ` Eric Dumazet [this message]
2014-09-06 16:38                 ` Eric Dumazet
2014-09-06 18:21                   ` Eric Dumazet
2014-09-07 19:05                     ` [PATCH net] ipv6: refresh rt6i_genid in ip6_pol_route() Eric Dumazet
2014-09-07 22:54                       ` David Miller
2014-09-08  4:18                         ` Eric Dumazet
2014-09-08  4:27                           ` David Miller
2014-09-08  4:43                             ` Eric Dumazet
2014-09-08  4:59                               ` David Miller
2014-09-08  5:07                                 ` Eric Dumazet
2014-09-08  8:11                                   ` Nicolas Dichtel
2014-09-08 10:28                                     ` Eric Dumazet
2014-09-08 12:16                                       ` Nicolas Dichtel
2014-09-08 18:48                                   ` Vlad Yasevich
2014-09-09 12:58                                   ` Hannes Frederic Sowa
2014-09-10  9:31                                     ` [PATCH net-next] ipv6: implement rt_genid_bump_ipv6 with fn_sernum and remove rt6i_genid Hannes Frederic Sowa
2014-09-10 13:26                                       ` Vlad Yasevich
2014-09-10 13:42                                         ` Hannes Frederic Sowa
2014-09-10 20:09                                       ` David Miller
2014-09-11  8:30                                         ` Hannes Frederic Sowa
2014-09-11 12:22                                           ` Vlad Yasevich
2014-09-11 12:40                                             ` Hannes Frederic Sowa
2014-09-11 12:05                                         ` Hannes Frederic Sowa
2014-09-11 14:19                                           ` Vlad Yasevich
2014-09-11 14:32                                             ` Hannes Frederic Sowa
2014-09-11 14:44                                               ` Vlad Yasevich
2014-09-11 14:47                                                 ` Hannes Frederic Sowa
2014-09-08 15:06               ` [PATCH v2 net-next] tcp: remove dst refcount false sharing for prequeue mode Eric Dumazet
2014-09-08 21:21                 ` David Miller
2014-09-08 21:30                   ` Eric Dumazet
2014-09-08 22:41                     ` David Miller
2014-09-09 23:56                     ` David Miller
2014-08-15 17:15       ` Performance regression on kernels 3.10 and newer Alexander Duyck
2014-08-15 17:59         ` Eric Dumazet
2014-08-15 18:49         ` Tom Herbert
2014-08-15 19:10           ` Alexander Duyck
2014-08-15 22:16             ` Tom Herbert
2014-08-15 23:23               ` Alexander Duyck
2014-08-18  9:03                 ` David Laight
2014-08-18 15:22                   ` Alexander Duyck
2014-08-18 15:29                     ` Rick Jones
2014-08-21 23:51         ` David Miller
2014-08-14 23:48     ` Eric Dumazet
2014-08-15  0:33       ` Rick Jones

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