On 5/12/06, Stephen Hemminger <shemminger@xxxxxxxx> wrote:
> Questions: > -------------- > > 1) Am I missing or misunderstanding something ? Linux does autotuning of send and receive buffer size.
Since the buffer sizes are set manually via a setsockopt() call, isn't autotuning supposed to be disabled ?
> 2) Do you have any other ideas which could explain the low percentage reached ? Max is limited by tcp_rmem/tcp_wmem, read Documenation/networking/ip-sysctl.txt
Indeed, but aren't tcp-rmem/tcp_wmem taken into account only when autotuning is enabled ? Besides since I have set net.ipv4.tcp_moderate_rcvbuf = 0 , shouldn't the receiver's autotuning be disabled ?
> 4) Why is the advertized window steadily growing until it reaches 6 > MBytes instead of being given directly a size of 6 Mbytes at the > beginning of the connection ? Slow start and autotuning.
Given the experiment's settings, I believe that autotuning is disabled (cf. 1), 2)) Isn't slow-start a tcp sender's side mechanism ?
> 5) Why does the advertized window remain stuck at 6 MBytes ? tcp_wmem
Autotuning is normaly disabled (cf. 1), 2), 4)) According to man tcp, it seems that by default linux tcp reserves 1/4 of the receive buffer for buffering overhead. This is conditioned by tcp_adv_win_scale variable. Thus, the "real" receive buffer size is actually 12 Mbytes from which only half is advertised ... Still it doesn't explain why only half is advertised ... As for the sender's side, I still don't get how the tcp send buffer is managed. Constantinos - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
