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Thread: TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

  1. #1
    Will Guest

    TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

    We are having severe file server performance issues in a Windows network,
    and I need some help in diagnosing behavior I am seeing.

    Windows 2003 clients and servers can alter the default TCP ACK frequency by
    setting a value named TcpAckFrequency for each specific adapter located in
    the registry key:

    \\HKLM\system\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{999...999}

    The value of TcpAckFrequency is the number of packets after which a TCP ACK
    is sent. Higher values for TcpAckFrequency mean fewer ACKs are being sent
    out.

    In the following report, the client is Windows 2003 and the server is
    Windows 2000. I can change TCP ACK behavior on the client and not on the
    server. Server runs on a 10/100 ethernet and client is on a gigabit
    ethernet.

    On the client, TcpAckFrequency defaults to 2. At this setting, copying a
    250 MB file from the server takes 45 seconds. That's not a terrible
    result, but I'm just establishing a baseline.

    Microsoft Windows 2003 performance guidelines recommends a setting for TCP
    ACK of 13 for gigabit Ethernet. Setting TcpAckFrequency to 13 on the
    client yields copy time of 20+ minutes!!

    Microsoft recommends a TCP ACK setting of 5 for 10/100 networks. Setting
    to 5 yields copy time of 18 minutes!!

    I tried going the other direction and setting to TcpAckFrequency of 1.
    This yields copy time of 2 minutes.

    Finally, I tried setting to TcpAckFrequency of 3. This yields copy time of
    13 minutes.

    Can someone explain to me why increasing the TcpAckFrequency even slightly
    is completely destroying performance of this file copy? The result is
    very surprising to me.

    On a related note, I am looking for a TCP expert who is also a Windows
    networking expert in the South San Francisco Bay Area to help us out on this
    problem. We are having numerous strange anomalies, including file copies
    that just terminate without finishing, and it is obvious something fairly
    serious is broken. If you are interested in doing that work as a
    contractor please forward resume to westes AT earthbroadcast.com.

    --
    Will



  2. #2
    Arkady Frenkel Guest

    Re: TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

    Setting TcpAckFrequency to 13 mean that you ignore delault TcpDelAckTicks of
    200 ms and miniport send it after 13 packets, so maybe such delay much
    bigger than 200 ms, only after that ( due to Nagle algorithm ) peer can
    continue to send next packet of the data.
    You can remove Nagle on peer socket and check what happen but that generally
    strongly not recommended practice.
    Arkady

    "Will" <westes-usc@noemail.nospam> wrote in message
    news:J_OdncVL4pC3nZfbnZ2dnUVZ_qarnZ2d@giganews.com...
    > We are having severe file server performance issues in a Windows network,
    > and I need some help in diagnosing behavior I am seeing.
    >
    > Windows 2003 clients and servers can alter the default TCP ACK frequency
    > by setting a value named TcpAckFrequency for each specific adapter located
    > in the registry key:
    >
    > \\HKLM\system\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{999...999}
    >
    > The value of TcpAckFrequency is the number of packets after which a TCP
    > ACK is sent. Higher values for TcpAckFrequency mean fewer ACKs are being
    > sent out.
    >
    > In the following report, the client is Windows 2003 and the server is
    > Windows 2000. I can change TCP ACK behavior on the client and not on the
    > server. Server runs on a 10/100 ethernet and client is on a gigabit
    > ethernet.
    >
    > On the client, TcpAckFrequency defaults to 2. At this setting, copying a
    > 250 MB file from the server takes 45 seconds. That's not a terrible
    > result, but I'm just establishing a baseline.
    >
    > Microsoft Windows 2003 performance guidelines recommends a setting for TCP
    > ACK of 13 for gigabit Ethernet. Setting TcpAckFrequency to 13 on the
    > client yields copy time of 20+ minutes!!
    >
    > Microsoft recommends a TCP ACK setting of 5 for 10/100 networks. Setting
    > to 5 yields copy time of 18 minutes!!
    >
    > I tried going the other direction and setting to TcpAckFrequency of 1.
    > This yields copy time of 2 minutes.
    >
    > Finally, I tried setting to TcpAckFrequency of 3. This yields copy time
    > of 13 minutes.
    >
    > Can someone explain to me why increasing the TcpAckFrequency even slightly
    > is completely destroying performance of this file copy? The result is
    > very surprising to me.
    >
    > On a related note, I am looking for a TCP expert who is also a Windows
    > networking expert in the South San Francisco Bay Area to help us out on
    > this problem. We are having numerous strange anomalies, including file
    > copies that just terminate without finishing, and it is obvious something
    > fairly serious is broken. If you are interested in doing that work as a
    > contractor please forward resume to westes AT earthbroadcast.com.
    >
    > --
    > Will
    >




  3. #3
    Will Guest

    Re: TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

    "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
    news:OwsQ%23VRcHHA.4888@TK2MSFTNGP02.phx.gbl...
    > Setting TcpAckFrequency to 13 mean that you ignore delault TcpDelAckTicks
    > of 200 ms and miniport send it after 13 packets, so maybe such delay much
    > bigger than 200 ms, only after that ( due to Nagle algorithm ) peer can
    > continue to send next packet of the data.
    > You can remove Nagle on peer socket and check what happen but that
    > generally strongly not recommended practice.


    How would I remove Nagle on the peer socket?

    --
    Will



  4. #4
    Arkady Frenkel Guest

    Re: TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

    SO_NODELAY option set on the socket with setsockopt()
    Arkady

    "Will" <westes-usc@noemail.nospam> wrote in message
    news:07-dnVTrpqJEYJfbnZ2dnUVZ_h6vnZ2d@giganews.com...
    > "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
    > news:OwsQ%23VRcHHA.4888@TK2MSFTNGP02.phx.gbl...
    >> Setting TcpAckFrequency to 13 mean that you ignore delault TcpDelAckTicks
    >> of 200 ms and miniport send it after 13 packets, so maybe such delay much
    >> bigger than 200 ms, only after that ( due to Nagle algorithm ) peer can
    >> continue to send next packet of the data.
    >> You can remove Nagle on peer socket and check what happen but that
    >> generally strongly not recommended practice.

    >
    > How would I remove Nagle on the peer socket?
    >
    > --
    > Will
    >
    >




  5. #5
    Will Guest

    Re: TCP Acknowledgement Frequency Configuration and Need Consultant in San Jose Area

    > "Will" <westes-usc@noemail.nospam> wrote in message
    > news:07-dnVTrpqJEYJfbnZ2dnUVZ_h6vnZ2d@giganews.com...
    >> "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
    >> news:OwsQ%23VRcHHA.4888@TK2MSFTNGP02.phx.gbl...
    >>> Setting TcpAckFrequency to 13 mean that you ignore delault
    >>> TcpDelAckTicks of 200 ms and miniport send it after 13 packets, so maybe
    >>> such delay much bigger than 200 ms, only after that ( due to Nagle
    >>> algorithm ) peer can continue to send next packet of the data.
    >>> You can remove Nagle on peer socket and check what happen but that
    >>> generally strongly not recommended practice.

    >>
    >> How would I remove Nagle on the peer socket?



    "Arkady Frenkel" <arkadyf@hotmailxdotx.com> wrote in message
    news:egeYzpccHHA.648@TK2MSFTNGP04.phx.gbl...
    > SO_NODELAY option set on the socket with setsockopt()
    > Arkady


    So obviously this isn't a practical solution for any problem I presented.
    I'm not going to rewrite Microsoft's code, and the problem I reported was
    with the COPY command and any other process that uses the OS primitives
    required for file copying from a file server to a client.

    --
    Will



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