[netperf-talk] netperf2.4.4 on linux, socket size issue ?

[mark wagner]

Hi I'm seeing an apparent drop in performance when specifying socket 
size while using netperf 2.4.4 on rhel5.2.  If I use -s to specify the 
size of the local socket during a TCP_STREAM test the throughput goes 
down by a factor of three for what would appear to be the same size socket.


[root at specclient2 np2.4]# ./netperf -P1 -l 20 -H 192.168.10.10 -- -m 16K 
-s 8K
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.10.10 
(192.168.10.10) port 0 AF_INET : spin interval : demo
Recv   Send    Send                         
Socket Socket  Message  Elapsed             
Size   Size    Size     Time     Throughput 
bytes  bytes   bytes    secs.    10^6bits/sec 

 87380  16384  16384    20.00    1389.43  

[root at specclient2 np2.4]# ./netperf -P1 -l 20 -H 192.168.10.10 -- -m 16K
TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.10.10 
(192.168.10.10) port 0 AF_INET : spin interval : demo
Recv   Send    Send                         
Socket Socket  Message  Elapsed             
Size   Size    Size     Time     Throughput 
bytes  bytes   bytes    secs.    10^6bits/sec 

 87380  16384  16384    20.00    4562.66  

 From the output, it would appear that both tests report that they are 
using the same buffer and message sizes, thus I would expect similar 
results.

I recall reading in the release notes that the buffer returned by 
getsock opt under Linux actually doubled the size of the socket 
requested, hence I'm using -s 8K to get a 16K socket in the first run 
above.  So, is the drop in performance because I'm really only using an 
8K buffer even though its getting reported as 16K or is something else 
going on here that I'm oblivious to?

thanks
-mark