lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:	Sat, 27 Sep 2014 09:46:25 -0700
From:	Eric Dumazet <>
To:	Eric Dumazet <>
Cc:	"David S. Miller" <>,,
	Yuchung Cheng <>,
	Neal Cardwell <>,
	Christoph Paasch <>
Subject: Re: [PATCH v3 net-next 3/3] tcp: better TCP_SKB_CB layout to reduce
 cache line misses

On Thu, 2014-09-25 at 13:14 -0700, Eric Dumazet wrote:
> TCP maintains lists of skb in write queue, and in receive queues
> (in order and out of order queues)
> Scanning these lists both in input and output path usually requires
> access to skb->next, TCP_SKB_CB(skb)->seq, and TCP_SKB_CB(skb)->end_seq
> These fields are currently in two different cache lines, meaning we
> waste lot of memory bandwidth when these queues are big and flows
> have either packet drops or packet reorders.
> We can move TCP_SKB_CB(skb)->header at the end of TCP_SKB_CB, because
> this header is not used in fast path. This allows TCP to search much faster
> in the skb lists.
> Even with regular flows, we save one cache line miss in fast path.
> Thanks to Christoph Paasch for noticing we need to cleanup
> skb->cb[] (IPCB/IP6CB) before entering IP stack in tx path,
> and that I forgot IPCB use in tcp_v4_hnd_req() and tcp_v4_save_options().
> Signed-off-by: Eric Dumazet <>
> ---

Silly me, I'll send a v4, sorry for the noise

net/ipv4/tcp_ipv4.c: In function 'tcp_v4_save_options':
net/ipv4/tcp_ipv4.c:889:33: warning: initialization from incompatible pointer type [enabled by default]
net/ipv4/tcp_ipv4.c: In function 'tcp_v4_hnd_req':
net/ipv4/tcp_ipv4.c:1432:43: warning: passing argument 3 of 'cookie_v4_check' from incompatible pointer type [enabled by default]
In file included from net/ipv4/tcp_ipv4.c:69:0:
include/net/tcp.h:474:14: note: expected 'struct ip_options *' but argument is of type 'struct inet_skb_parm *'

To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists