why my dummynet queue not work?

[Brooks Davis]

On Fri, Mar 11, 2005 at 12:03:01PM +0800, jim song wrote:
> Hi, 
> I encounter a problem when using dummynet to test tcp throughputs.
> 
> I used a freebsd box running dummynet as an router. And all my testing
> machines are attached to giga switch.
> 
> On the router, I use dummynet to emulate a long-fat network which has 
> high bandwidth but long delays. The setting is as attached. I have modified
> related configuration and source files and reinstall the kernel.
> 
> The problem is that the tcp throughput through this router could not 
> reach reasonable value. I can only get 5Mbps throughputs. (I have set the tcp
> window to 5MBytes already). It seems like that the queue parameter
> doesnot work. Because if it works, the throughputs will go up to the 
> bandwidth limitation.

Why are you using the queue parameter at all?  If you just want to
emulate a pipe there is usually no need to do that.  Have you adjusted
your socket buffers in addition to your max TCP window size?

-- Brooks

> Could somebody tell me why?
> 
> Thanks,
> --Jim
> 
> 
> 
> --------------------------------------------------
> ipfw -f -q flush
> ipfw -f -q pipe flush
> ipfw add pipe 1 ip from any to any in recv em0
> ipfw add pipe 2 ip from any to any out xmit em0
> ipfw pipe 1 config bw 200Mbit/s delay 25ms queue 1000
> ipfw pipe 2 config bw 200Mbit/s delay 25ms queue 1000
> 
> # 1. compiling Kernel Options
> # options IPFIREWALL
> # options IPFIREWALL_DEFAULT_TO_ACCEPT
> # options DUMMYNET
> # options HZ=1000
> # options NMBCLUSTERS=131072
> # options DEVICE_POLLING
> 
> # 2. Add the following lines into /etc/sysctl.conf
> # kern.polling.enable=1
> # kern.polling.user_frac=5
> # kern.polling.burst_max=400
> # kern.polling.each_burst=15
> # net.inet.ip.intr_queue_maxlen=3000
> 
> # 3. Modify source code of ipfw and dummynet to support larger queue size
> 
> # 4. Increase NIC buffer by setting EM_MAX_RXD to 4096 in
> /usr/src/sys/dev/em/if_em.h
> 
> --------------------------------------------------------------------
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