netdev - Re: [PATCH v4 net-next 0/3] tcp: Make use of MSG_EOR in tcp

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Date:	Mon, 25 Apr 2016 20:50:02 -0400
From:	Soheil Hassas Yeganeh <soheil@...gle.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v4 net-next 0/3] tcp: Make use of MSG_EOR in tcp_sendmsg

On Mon, Apr 25, 2016 at 5:44 PM, Martin KaFai Lau <kafai@...com> wrote:
> v4:
> ~ Do not set eor bit in do_tcp_sendpages() since there is
>   no way to pass MSG_EOR from the userland now.
> ~ Avoid rmw by testing MSG_EOR first in tcp_sendmsg().
> ~ Move TCP_SKB_CB(skb)->eor test to a new helper
>   tcp_skb_can_collapse_to() (suggested by Soheil).
> ~ Add some packetdrill tests.

Thanks for the nice patches and the tests!

> v3:
> ~ Separate EOR marking from the SKBTX_ANY_TSTAMP logic.
> ~ Move the eor bit test back to the loop in tcp_sendmsg and
>   tcp_sendpage because there could be >1 threads doing
>   sendmsg.
> ~ Thanks to Eric Dumazet's suggestions on v2.
> ~ The TCP timestamp bug fixes are separated into other threads.
>
> v2:
> ~ Rework based on the recent work
>   "add TX timestamping via cmsg" by
>   Soheil Hassas Yeganeh <soheil.kdev@...il.com>
> ~ This version takes the MSG_EOR bit as a signal of
>   end-of-response-message and leave the selective
>   timestamping job to the cmsg
> ~ Changes based on the v1 feedback (like avoid
>   unlikely check in a loop and adding tcp_sendpage
>   support)
> ~ The first 3 patches are bug fixes.  The fixes in this
>   series depend on the newly introduced txstamp_ack in
>   net-next.  I will make relevant patches against net after
>   getting some feedback.
> ~ The test results are based on the recently posted net fix:
>   "tcp: Fix SOF_TIMESTAMPING_TX_ACK when handling dup acks"
>
> One potential use case is to use MSG_EOR with
> SOF_TIMESTAMPING_TX_ACK to get a more accurate
> TCP ack timestamping on application protocol with
> multiple outgoing response messages (e.g. HTTP2).
>
> One of our use case is at the webserver.  The webserver tracks
> the HTTP2 response latency by measuring when the webserver sends
> the first byte to the socket till the TCP ACK of the last byte
> is received.  In the cases where we don't have client side
> measurement, measuring from the server side is the only option.
> In the cases we have the client side measurement, the server side
> data can also be used to justify/cross-check-with the client
> side data.
>