From: David Miller <[EMAIL PROTECTED]> Date: Tue, 31 Oct 2006 17:30:28 -0800 (PST)
> From: Stephen Hemminger <[EMAIL PROTECTED]> > Date: Tue, 31 Oct 2006 16:10:07 -0800 > > > On Tue, 31 Oct 2006 15:25:16 -0800 > > "Xiaoliang (David) Wei" <[EMAIL PROTECTED]> wrote: > > > > > It seems that the default Vegas alpha parameter in the rc4 is 1... > > > > > > I observed similar situation with the NS2Linux simulator (with 2.6.16 > > > code) and found that if alpha=1, delayed ack will make it broken > > > (keeping cwnd very low without real congestion) > > > > > > See details at > > > http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegas > > > > > > (Basically alpha==1 means Vegas seeks to see a delay of about 1 packet > > > worth. With delayed ack, 1 packet worth of delay is common even with > > > no congestion.) > > > > > > To make Vegas work, I'd suggest to raise alpha to at least 2 or 3. > > > (and beta has to be at least as large as alpha.) > > > > > > -David > > > > > > > I ran with the current default: > > alpha = 1 (scaled 2) > > beta = 3 (scaled 6) > > gamma = 1 (scaled 2) > > Testing with alpha=2 and beta=4 would be interesting. Instead of letting this issue rot, I've checked the following into net-2.6.20 commit cd7f265b9069d8fd66a33d37139821f84ef04f0e Author: David S. Miller <[EMAIL PROTECTED]> Date: Tue Nov 28 14:37:38 2006 -0800 [TCP] Vegas: Increase default alpha to 2 and beta to 4. This helps Vegas cope better with delayed ACKs, see analysis at: http://www.cs.caltech.edu/%7Eweixl/technical/ns2linux/known_linux/index.html#vegas Signed-off-by: David S. Miller <[EMAIL PROTECTED]> diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c index a3b7aa0..ddc4bcc 100644 --- a/net/ipv4/tcp_vegas.c +++ b/net/ipv4/tcp_vegas.c @@ -42,8 +42,8 @@ #include <net/tcp.h> * with V_PARAM_SHIFT bits to the right of the binary point. */ #define V_PARAM_SHIFT 1 -static int alpha = 1<<V_PARAM_SHIFT; -static int beta = 3<<V_PARAM_SHIFT; +static int alpha = 2<<V_PARAM_SHIFT; +static int beta = 4<<V_PARAM_SHIFT; static int gamma = 1<<V_PARAM_SHIFT; module_param(alpha, int, 0644); - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
