netdev - Re: [PATCH net-next 0/6] net: make TCP preemptible

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Message-ID: <20160428211839.GB2276@localhost.localdomain>
Date:	Thu, 28 Apr 2016 18:18:39 -0300
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	"David S . Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 0/6] net: make TCP preemptible

On Wed, Apr 27, 2016 at 10:25:46PM -0700, Eric Dumazet wrote:
> Most of TCP stack assumed it was running from BH handler.
> 
> This is great for most things, as TCP behavior is very sensitive
> to scheduling artifacts.
> 
> However, the prequeue and backlog processing are problematic,
> as they need to be flushed with BH being blocked.
> 
> To cope with modern needs, TCP sockets have big sk_rcvbuf values,
> in the order of 16 MB.
> This means that backlog can hold thousands of packets, and things
> like TCP coalescing or collapsing on this amount of packets can
> lead to insane latency spikes, since BH are blocked for too long.

And due to that, it may potentially lead to packet drops on NIC ring
buffers.  Great, thanks Eric.

> It is time to make UDP/TCP stacks preemptible.
> 
> Note that fast path still runs from BH handler.
> 
> Eric Dumazet (6):
>   tcp: do not assume TCP code is non preemptible
>   tcp: do not block bh during prequeue processing
>   dccp: do not assume DCCP code is non preemptible
>   udp: prepare for non BH masking at backlog processing
>   sctp: prepare for socket backlog behavior change
>   net: do not block BH while processing socket backlog
> 
>  net/core/sock.c          |  22 +++------
>  net/dccp/input.c         |   2 +-
>  net/dccp/ipv4.c          |   4 +-
>  net/dccp/ipv6.c          |   4 +-
>  net/dccp/options.c       |   2 +-
>  net/ipv4/tcp.c           |   6 +--
>  net/ipv4/tcp_cdg.c       |  20 ++++----
>  net/ipv4/tcp_cubic.c     |  20 ++++----
>  net/ipv4/tcp_fastopen.c  |  12 ++---
>  net/ipv4/tcp_input.c     | 126 +++++++++++++++++++----------------------------
>  net/ipv4/tcp_ipv4.c      |  14 ++++--
>  net/ipv4/tcp_minisocks.c |   2 +-
>  net/ipv4/tcp_output.c    |   7 ++-
>  net/ipv4/tcp_recovery.c  |   4 +-
>  net/ipv4/tcp_timer.c     |  10 ++--
>  net/ipv4/udp.c           |   4 +-
>  net/ipv6/tcp_ipv6.c      |  12 ++---
>  net/ipv6/udp.c           |   4 +-
>  net/sctp/inqueue.c       |   2 +
>  19 files changed, 124 insertions(+), 153 deletions(-)
> 
> -- 
> 2.8.0.rc3.226.g39d4020
>