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 > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
