Re: [LARTC] TC (HTB) doesn't work well when network is congested?

[William Xu <wxu@max-t.com>]

Thanks, Peter,

So what you means is that network congestion caused my problem. I test 
the bandwidth
between client1 and server using iperf, SEND and RECV are both 122MB/s.  
I tried
different values for the total bandwidth, and I got the following numbers:

total bandwidth 120MB/s    client1 SEND :10MB/s     RECV :39MB/s
total bandwidth 110MB/s    client1 SEND :16MB/s     RECV :40MB/s
total bandwidth 100MB/s    client1 SEND :30MB/s     RECV :38MB/s
total bandwidth   90MB/s    client1 SEND :39MB/s     RECV :40MB/s
total bandwidth   80MB/s    client1 SEND :39MB/s     RECV :40MB/s
total bandwidth   70MB/s    client1 SEND :40MB/s     RECV :40MB/s
total bandwidth   60MB/s    client1 SEND :40MB/s     RECV :40MB/s

So TC works well as long as total bandwidth is below 90MB/s, which is 
about 70% of the
wise speed. Is it possible that I can use the full bandwidth (122MB/s) 
in my script?

william

Peter Rabbitson wrote:

> William Xu wrote:
>
>> Hi,
>>
>> I have a server and ten clients in a Gigabit network. The server has 
>> 125mbps network bandwidth.
>> I want that the server has 40Mbps bandwidth reserved for client 1 (IP 
>> 192.168.5.141), and the
>> rest bandwidth is for all other clients.
>>
>> <snip>
>>
>> I ran a test in which all 10 clients send/receive packets to/from the 
>> server simultaneously. But
>> Client 1 only got 20mbps bandwidth for sending, and 38mpbs for 
>> receiving. If I limit the rate of
>> both classes 1:1 to 60mbps instead of 125mbps, Client 1 got 39mbps 
>> for sending, and 40mbps for
>> receiving.
>>
>> I am not sure what might cause this. Is it because TC doesn't work 
>> well when network is congested?
>> Or my script is not right?
>>
>
> No network will be able to operate at its theoretical maximum. In the 
> case of a gigabit network you will be lucky to get consistent 120mbps, 
> and it heavily depends on the hardware quality, and the number of 
> switches in between. So what you are doing is oversaturating the link, 
> the ACK packets can not get through, your speed drops due to 
> delays/retransmissions. Perform a test with only two systems sending 
> stuff to each other to see what is the actual bandwidth you can hope 
> for, and use that number instead of 125mbps.


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