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Message-ID: <20100914093758.GA24348@ms2.inr.ac.ru> Date: Tue, 14 Sep 2010 13:37:58 +0400 From: Alexey Kuznetsov <kuznet@....inr.ac.ru> To: David Miller <davem@...emloft.net> Cc: ilpo.jarvinen@...sinki.fi, eric.dumazet@...il.com, leandroal@...il.com, netdev@...r.kernel.org Subject: Re: TCP packet size and delivery packet decisions Hello! > Therefore, how about the following? This will work. There is one trap though. If pktsize > max_window, packets never will be transmitted in normal path, only from probe timer, which will be very slow. If we do not want to mess with tcp_write_xmit(), it is still possible to relax the bound to tp->max_window. (BTW, this even does not contradict to RFC, only Fs = 1 for tiny windows). This should work: diff --git a/include/net/tcp.h b/include/net/tcp.h index 34f5cc2..8cf8cdb 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -501,8 +501,22 @@ extern unsigned int tcp_current_mss(struct sock *sk); /* Bound MSS / TSO packet size with the half of the window */ static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize) { - if (tp->max_window && pktsize > (tp->max_window >> 1)) - return max(tp->max_window >> 1, 68U - tp->tcp_header_len); + int cutoff; + + /* When peer uses tiny windows, there is no use in packetizing + * to sub-MSS pieces for the sake of SWS or making sure there + * are enough packets in the pipe for fast recovery. + * + * On the other hand, for extremely large MSS devices, handling + * smaller than MSS windows in this way does make sense. + */ + if (tp->max_window >= 512) + cutoff = (tp->max_window >> 1); + else + cutoff = tp->max_window; + + if (cutoff && pktsize > cutoff) + return max(cutoff, 68U - tp->tcp_header_len); else return pktsize; } -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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