linux-kernel - Re: [RFC] [TCP 1/3] tcp: Add MSG_NEW_PACKET flag to indicate preferable packet boundaries

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Date:	Fri, 29 Jun 2012 17:11:06 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andreas Gruenbacher <agruen@...bit.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC] [TCP 1/3] tcp: Add MSG_NEW_PACKET flag to indicate
 preferable packet boundaries

On Fri, 2012-06-29 at 16:54 +0200, Andreas Gruenbacher wrote:
> The MSG_NEW_PACKET flag indicates to sendmsg / sendpage that the message or
> page should be put into a new packet even when there is still room left in the
> previous packet.
> 
> In the tcp protocol, messages which are not sent immediately are queued.  When
> more data is sent, it will be added to the last segment in that queue until
> that segment is "full" whenever possible; only then is a new segment added.
> Right now, there is no way to indicate when tcp should start a new segment.
> The new flag allows to control that.
> 
> Signed-off-by: Andreas Gruenbacher <agruen@...bit.com>
> ---

I don't understand how maintaining any message boundaries at sender can
prevent any middlebox or the receiver to coalesce frames to any
boundaries it prefers ?



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