netdev - Re: [RFC PATCH net-next 0/3] sctp: add GSO support

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Message-ID: <20160128210326.GD6602@mrl.redhat.com>
Date:	Thu, 28 Jan 2016 19:03:26 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Michael Tuexen <Michael.Tuexen@...chi.franken.de>
Cc:	David Laight <David.Laight@...LAB.COM>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Neil Horman <nhorman@...driver.com>,
	Vlad Yasevich <vyasevich@...il.com>,
	David Miller <davem@...emloft.net>,
	"brouer@...hat.com" <brouer@...hat.com>,
	"alexander.duyck@...il.com" <alexander.duyck@...il.com>,
	"alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
	"borkmann@...earbox.net" <borkmann@...earbox.net>,
	"marek@...udflare.com" <marek@...udflare.com>,
	"hannes@...essinduktion.org" <hannes@...essinduktion.org>,
	"fw@...len.de" <fw@...len.de>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"john.r.fastabend@...el.com" <john.r.fastabend@...el.com>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 0/3] sctp: add GSO support

On Thu, Jan 28, 2016 at 06:54:06PM +0100, Michael Tuexen wrote:
> > On 28 Jan 2016, at 14:51, David Laight <David.Laight@...LAB.COM> wrote:
> > 
> > From: Marcelo Ricardo Leitner
> >> Sent: 27 January 2016 17:07
> >> This patchset is merely a RFC for the moment. There are some
> >> controversial points that I'd like to discuss before actually proposing
> >> the patches.
> > 
> > You also need to look at how a 'user' can actually get SCTP to
> > merge data chunks in the first place.
> > 
> > With Nagle disabled (and it probably has to be since the data flow
> > is unlikely to be 'command-response' or 'unidirectional bulk')
> > it is currently almost impossible to get more than one chunk
> > into an ethernet frame.
> > 
> > Support for MSG_MORE would help.
> What about adding support for the explicit EOR mode as specified in
> https://tools.ietf.org/html/rfc6458#section-8.1.26

Seizing the moment to clarify my understanding on that. :)
Such multiple calls to send system calls will result in a single data
chunk. Is that so? That's what I get from that text and also from this
snippet:
"Sending a message using sendmsg() is atomic unless explicit end of
record (EOR) marking is enabled on the socket specified by sd (see
Section 8.1.26)."

Best regards,
Marcelo

> Best regards
> Michael
> > 
> > Given the current implementation you can get almost the required
> > behaviour by turning nagle off and on repeatedly.
> > 
> > I did wonder whether the queued data could actually be picked up
> > be a Heartbeat chunk that is probing a different remote address
> > (which would be bad news).
> > 
> > 	David
> > 
> > --
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> > 
>