From: Christoph Paasch <christoph.paasch@uclouvain•be>
To: Eric Dumazet <edumazet@google•com>
Cc: "David S. Miller" <davem@davemloft•net>,
netdev@vger•kernel.org, Yuchung Cheng <ycheng@google•com>,
Neal Cardwell <ncardwell@google•com>
Subject: Re: [PATCH net-next 3/3] tcp: better TCP_SKB_CB layout to reduce cache line misses
Date: Tue, 23 Sep 2014 09:20:16 +0200 [thread overview]
Message-ID: <20140923072016.GL3291@cpaasch-mac> (raw)
In-Reply-To: <1411429844-11099-4-git-send-email-edumazet@google.com>
Hello Eric,
On 22/09/14 - 16:50:44, 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.
>
> Signed-off-by: Eric Dumazet <edumazet@google•com>
> ---
> include/net/tcp.h | 12 ++++++------
> net/ipv4/tcp_ipv4.c | 7 +++++++
> net/ipv6/tcp_ipv6.c | 7 +++++++
> 3 files changed, 20 insertions(+), 6 deletions(-)
doesn't also the tx-path relies on IPCB(skb) being memset to 0 (e.g., in
xfrm4_output or ip_options_build)
Or is it somewhere already explicitly memset to 0? (didn't found this place
in the code though)
Cheers,
Christoph
next prev parent reply other threads:[~2014-09-23 7:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-22 23:50 [PATCH net-next 0/3] tcp: better TCP_SKB_CB layout Eric Dumazet
2014-09-22 23:50 ` [PATCH net-next 1/3] ipv4: rename ip_options_echo to __ip_options_echo() Eric Dumazet
2014-09-22 23:50 ` [PATCH net-next 2/3] ipv6: add a struct inet6_skb_parm param to ipv6_opt_accepted() Eric Dumazet
2014-09-22 23:50 ` [PATCH net-next 3/3] tcp: better TCP_SKB_CB layout to reduce cache line misses Eric Dumazet
2014-09-23 7:20 ` Christoph Paasch [this message]
2014-09-23 7:36 ` Christoph Paasch
2014-09-23 9:09 ` Eric Dumazet
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