netdev - RE: [PATCH net-next v3 3/3] net: sctp: Add support for MSG

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Date:	Tue, 22 Jul 2014 15:25:41 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Vlad Yasevich' <vyasevich@...il.com>,
	"Linux Networking Development Mailing List" <netdev@...r.kernel.org>,
	"'linux-sctp@...r.kernel.org'" <linux-sctp@...r.kernel.org>
CC:	David Miller <davem@...emloft.net>
Subject: RE: [PATCH net-next v3 3/3] net: sctp: Add support for MSG_MORE on
 SCTP

From: Vlad Yasevich
> On 07/22/2014 09:45 AM, David Laight wrote:
> > From: Vlad Yasevich
> >> On 07/22/2014 04:59 AM, David Laight wrote:
> >>> If MSG_MORE is set then the data chunk will be buffered until either
> >>> a full packet would be generated, or something causes a chunk to be
> >>> sent (eg data without MSG_MORE or a heartbeat).
> >>
> >> heartbeat will not cause a data flush.  Only SACKs do that as they control
> >> congestion and flow.
> >
> > Experimentally heartbeats cause data to be sent.
> > I'd only got one IP address at each end - so don't know what happens to
> > any 'probe' HBs.
> > I frigged my code to set MSG_MORE if the data chunk was over 200 bytes.
> > A single long fragment would be collected by a short one, or by a heartbeat.
> > I did wonder if that was a bug - but it would happen for data delayed by Nagle.
> 
> That sounds kind like a bug.  The end of packet usually causes a flush of the outqueue,
> but any delayed data shouldn't be sent as HB should not cause a data flush.

I think the data is already in the relevant queue, it would have been sent
earlier if there had been a packet with anything in it.
So maybe the HB does get bundled with pending data.

Try applying my patch and doing some simple tests...

	David



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