From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 26 Aug 2004 10:46:43 -0700 From: Eugene Surovegin To: "Smith, Craig" Cc: linuxppc-embedded@lists.linuxppc.org Subject: Re: UDP packet loss (8xx/2.4.26) Message-ID: <20040826174642.GB16665@gate.ebshome.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: On Thu, Aug 26, 2004 at 09:35:17AM -0700, Smith, Craig wrote: > > Hello, > I'm having a problem with UDP packet loss (small packets, simulated > compressed VoIP calls). The packets are being dropped in netif_rx, > and if I increase the netdev_max_backlog to something huge I get > no packet loss, but the delay is pretty bad resulting in terrible > MOS scores. > > I'm trying to decide if my Linux kernel simply can't keep up > with the traffic or if there's still something I can tweak to > improve the performance (or maybe I need to try getting a 2.6 > kernel to work). It's very unlikely 2.6 will make things better. > Below, I've included a few more details about > my platform and test setup. The test runs fine on the same > board with our proprietary OS, so I know it's "physically" > possible, I'm just evaluating Linux's performance as well. > > Kernel: 2.4.26 (kernel.org) w/ mpc860sar (from sourceforge.net) > CPU: 855T @ 48MHz This is very low-end CPU :) > MEM: 16M SDRAM, 4M flash > LAN: Broadcom BCM5327 10/100 8 port switch > WAN: Conexant Bt8370 T1 (ATM using mpc860sar code) > > Test: 30 compressed voice calls downstream (LAN<-WAN) > Packet size: ~64bytes IP/UDP + ATM overhead > In a 30 second test, the test sends ~45000 packets (30 different > streams), and about 5000 are dropped (unless I increase the > netdev_max_backlog which just delays the inevitable dropping). > > I believe the T1/ATM interface is working fine, I found the source > of the dropped packets in /proc/net/softnet_stat so that made me > wonder if the kernel was simply not keeping up. > > Should I expect to see this kind of loss with a 2.4 kernel? > Is it just a matter of tweaking some more networking related parameters? > Should I be using another distribution of kernel source? I think you have to work on network driver, make it use NAPI (http://www.usenix.org/publications/library/proceedings/als01/jamal.html) and this _may_ help. Using very slow processor without NAPI-enabled net driver is the main cause of big packet loss on RX path. -- Eugene ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/