Re: select()/socket has problems under 2.2.x.

Alan Cox (
Tue, 27 Apr 1999 18:49:28 +0100 (BST)

> 1. When txqueuelen is set low (e.g. <=10) the queue into the ppp0 device overflows and packets are
> occasionally lost. This explains the mysterious missing-packet problem I provided tcpdumps for.
> Increasing txqueuelen "fixed" that problem.

You want to lower it (see 3)

> retrain, which lasts a few seconds each, the errored bits cause an internal modem retransmit,
> delaying logical delivery of the data to Linux by a few hundred milliseconds at a time. This timing
> variability, which is not Linux's fault, exacerbates (I hypothesize) a third problem:

If you get a lot of retrains fix your phone line 8) but also check your
manuals. You can tell the modem to refuse to retrain down a speed but to
keep the current speed on most modems.

> ensure that packets aren't dropped due to overflows of the outgoing buffer? If not, wouldn't it be
> better to keep txquueuelen high and just grin and bear the latency for interactive use?

Generally lower txqlen is better. It speeds up feedback

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at