[e2e] query reg improving TCP performane

Hi All,

  I was doing some Bandwidth measurement test on a 100 mbs link with a RTT of about 70ms.
  Based on that, I calculated the BDP as follows.

          BDP = Bandwidth * RTT
              = 13107200 bytes * .07 secs
              = 896 Kbytes
              = 900 Kbyes (approx)
              = 921600 bytes

   After that I adjusted the TCP window size as follows:

/proc/sys/net/core/rmem_max 921600
/proc/sys/net/core/wmem_max 921600
/proc/sys/net/ipv4/tcp_rmem 4096 87380 921600
/proc/sys/net/ipv4/tcp_wmem 4096 87380 921600

   These adjustmenst I had done on a Linux host with 2.6.15 kernel. The congestion

   control algorithm , it is using BIC

   The same window adjustments I had performed on the other hand on a Linux host

   with kernel 2.6.9 . It is also using BIC for congestion control.

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   The Bandwidth Performnce test I am doing using iperf , a highly popular public

   domain tool for measuring TCP & UDP Bandwidth Performance .

   With the default Linux 2.6 TCP window settings , I was getting a throughput of

   nearly 10mbs which is very low for a 100 mbs link.

   So , I performed the above TCP adjustmets and I found the throughput to be around

   55 mbs which is a significant improvement . But that is not fully utilsing the link

   as it is a dedicated link and there was no other traffic.    This , I proved with the next experiment where I reached a link utilisation of

   little more than 95 mbs . That is very much O.K for a 100mbs link.

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   I did the following adjustments. I increased the above calculated BDP by nearly

   half of the value . The TCP settings now look like this.

/proc/sys/net/core/rmem_max 175636
/proc/sys/net/core/wmem_max 175636
/proc/sys/net/ipv4/tcp_rmem 4096 87380 175636
/proc/sys/net/ipv4/tcp_wmem 4096 87380 175636

    After these settings , I find the link utilisation to be nearly 95 mbs.

    According to many papers that I read , I found that the BDP should be equal

    to the product of Bandwidth * RTT .
    I had done that , but the link utilisation is only 50%. But when I increased

    to a much higher value , the link utilisation is nearly around 95 %.

    I am confused regarding my findings.Please clarify me so that I can perform

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    the experiment correctly.

    With Thanks in Advance Received on Thu Jul 5 11:09:15 2007