Em Thu, Jan 03, 2008 at 11:19:32PM +0100, Tomasz Grobelny escreveu: > Dnia Thursday 03 January 2008, Arnaldo Carvalho de Melo napisał: > > Em Wed, Jan 02, 2008 at 11:34:25PM +0100, Tomasz Grobelny escreveu: > > > with speed at which packets can be transmitted over the network. Is it > > > the case for dccp as well? If so, does it mean that provided stable > > > network conditions over longer period of time and using blocking version > > > of sendmsg in a loop very few packets should be lost? (By very few I mean > > > < 10%) > > > > If the application sends many packets in rapid succession before the > > DCCP core gets permission from the CCID in use to send those packets to > > the network what will happen is that sk_write_queue will have packets > > waiting, using the memory allowed to be allocated for the socket send > > buffer, which will make sock_alloc_send_skb wait for the packets in > > sk_write_queue to be sent, freeing up send buffer space, when it will be > > possible for sock_alloc_send_skb to actually allocate memory for the > > packet and return to dccp_sendmsg, that in turn will return to the > > application after putting the newly allocated packet in sk_write_queue, > > doing the send buffer accounting and trying to send something in > > dccp_write_xmit, where it will ask the CCID if it can send some more > > packets, got it? > > > I think I almost got it. Thanks a lot for the detailed explanation. But I've > got two more questions: > 1. How can I control the amount of "memory allowed to be allocated for the > socket send buffer"? It it somehow connected with tx_qlen or is it not? setsockopt(socket_descriptor, SOL_SOCKET, SO_SNDBUF, ...) execute: man 7 socket /SO_SNDBUF tx_qlen is something experimental, system wide. > 2. If I decide that for whatever reason a given skb already in sk_write_queue > should not be transmitted I should remove it from queue and call kfree_skb on > it, it that right? There is no interface for that right now, once you pass a packet to the kernel, the application has no control over it anymore. But there has been talks about things like setting a timeout for packets to stay on the queue, or even for the app to have an interface for dropping packets from the head of the queue. - Arnaldo - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
