From: Vlad Yasevich > 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. In that case it is probably worth caching SCTP_NODELAY in the asoc as well. It looks like it ought to be valid for the setsockopt code to 'list_for_each_entry' on ep->asocs and sctp_endpoint_add_asoc() to copy down the current value. Should I change the code so that the first chunk is also not sent? If an application failed to do a final send (with MSG_MORE clear) then it would never be set, and there is no way to flush it. I didn't do that because I'm not really interested in merging 2 chunks. I'm trying to get 100s of chunks merged. 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
