Re: What exactly is net.inet.tcp.sockthreshold?
Re: What exactly is net.inet.tcp.sockthreshold?
- Subject: Re: What exactly is net.inet.tcp.sockthreshold?
- From: "Peter Sichel" <email@hidden>
- Date: Mon, 3 Oct 2005 09:21:54 -0400
On 10/2/05, Chris McFarling wrote:
>In my case, two clients send to the server simultaneously over our LAN (all
>are on gigabit). The transfer rate of each client drops to ~6-8MB/s.
>Whereas, each individual client is capable of sending to the same server at
>~30-40MB/s. While there is obviously going to be a decrease in performance
>when two Gb devices are sending to one Gb device, I would expect a better
>transfer rate than 6MB/s.
Yes. Since you previously observed that reducing the window size helped,
I inferred that perhaps ACKs are being delayed by other traffic.
>So anyway, based on the fact that the AFP server overrides the system
>default TCP window size by using SO_RCVBUF, is IPNetSentryX able to override
>that behavior of AFP?
Yes. IPNetSentryX uses an NKE to examine and modify the packets
at the data link layer. It does traffic shaping by modifying
the advertised window size of TCP ACK segments on the fly,
so it does indeed override the default behavior of AFP.
I've run a number of tests with AFP transfers and the results
are very consistent. AFP opens a single TCP connection when
a remote volume is mounted and uses that connection for all
transfers. One detail is to start IPNetSentryX before you
mount the remote volume so it can see the connection being
established. Otherwise it has to guess and adapt itself to
determine the window scale factor (which is sent as a TCP
option on the SYN segment).
FYI: You can try IPNetSentryX free for 21-days. The latest
candidate 1.3c8 includes the traffic shaping code. I haven't
tested it at gigabit speeds yet, but as an NKE it should be
quite fast. [I suspect an ipfw divert socket used by some
other implementations wouldn't help much at this speed.]
Kind Regards,
- Peter
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