From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH net-next v2 3/3] net: sctp: Add partial support for MSG_MORE on SCTP Date: Tue, 15 Jul 2014 11:24:29 -0400 Message-ID: <53C547AD.3090906@gmail.com> References: <063D6719AE5E284EB5DD2968C1650D6D1726EEB7@AcuExch.aculab.com> <53C04509.70304@gmail.com> <063D6719AE5E284EB5DD2968C1650D6D17271E0B@AcuExch.aculab.com> <53C42C58.3050108@gmail.com> <063D6719AE5E284EB5DD2968C1650D6D17273C31@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: "'davem@davemloft.net'" To: David Laight , "'netdev@vger.kernel.org'" , "'linux-sctp@vger.kernel.org'" Return-path: Received: from mail-qc0-f181.google.com ([209.85.216.181]:64649 "EHLO mail-qc0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755324AbaGOPYc (ORCPT ); Tue, 15 Jul 2014 11:24:32 -0400 In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D17273C31@AcuExch.aculab.com> Sender: netdev-owner@vger.kernel.org List-ID: On 07/15/2014 10:33 AM, David Laight wrote: > From: Vlad Yasevich >> On 07/14/2014 12:27 PM, David Laight wrote: >>> From: Vlad Yasevich >>> ... >>>>> + /* Setting MSG_MORE currently has the same effect as enabling Nagle. >>>>> + * This means that the user can't force bundling of the first two data >>>>> + * chunks. It does mean that all the data chunks will be sent >>>>> + * without an extra timer. >>>>> + * It is enough to save the last value since any data sent with >>>>> + * MSG_MORE clear will already have been sent (subject to flow control). >>>>> + */ >>>>> + if (msg->msg_flags & MSG_MORE) >>>>> + sp->tx_delay |= SCTP_F_TX_MSG_MORE; >>>>> + else >>>>> + sp->tx_delay &= ~SCTP_F_TX_MSG_MORE; >>>>> + >>>> >>>> This is ok for 1-1 sockets, but it doesn't really work for 1-many sockets. If one of >>>> the associations uses MSG_MORE while another does not, we'll see some interesting >>>> side-effects on the wire. >>> > ... >>> I don't think this is a problem. >> >> Not, it is not a _problem_, but it does make MSG_MORE rather useless >> in some situations. Waiting for an ACK across low-latency links >> is rare, but in a high-latency scenarios where you want to utilize the >> bandwidth better with bundling, you may not see the gains you expect. >> >> Since MSG_MORE is association, it should be handled as such and an >> a change on one association should not effect the others. > > I think the comments already say that it is only a partial implementation. > (If you send 2 chunks on an idle connection, they get sent separately.) > Perhaps I'll add a note about possibly 'odd' effects for 1-many sockets > with multi-threaded apps. > > It helps a lot for my M3UA traffic. > I can get the same effect on an old kernel by repeatedly changing SCTP_NODELAY, > but that does rather rely on the way Nagle is implemented. You can fix this by having an sp->tx_delay value and a assoc->tx_delay value and simple check (sp->tx_delay | assoc->tx_delay). MSG_MORE would only set the assoc->tx_delay while SCTP_NODELAY would effect the socket. This way, when one association uses MSG_MORE, it will not effect other associations on the same socket that don't use it. -vlad > > David > > > >