[REBOL] Re: Rugby / TCP woes
From: petr:krenzelok:trz:cz at: 27-Nov-2001 18:06
[holger--rebol--com] wrote:
>On Tue, Nov 27, 2001 at 02:14:47PM +0100, Petr Krenzelok wrote:
>
>>1) Yes, it should not be slower in any way imo! TCP connection is no magic - just
>>raw packets on network. In reality, it should be just reverse - to set-up TCP
>>connection, machine requesting connection sends SYN packet, remote machine sends
>>SYN, ACK packet, acknowledging connection acceptance, then first machine once
>>again confirms by ACK packet - so, actually setting-up tcp connection is three
>>way process, while sending packet containing data means sending PSH, ACK with
>>data, while other side is confirming with ACK, or PUSH, ACK, if sending data too
>>... or something like that ...
>>
>
>More or less, although there are some subtle differences, e.g. in the
>ACK delay strategy, in buffer sizes and in the precise behavior of the
>Nagle algorithm. Also, the PSH flag is implemented very inconsistently
>across platforms. All of these issues can affect performance, in
>particular for asynchronous, full-duplex communication.
>
>One thing you can try is "error? try [set-modes port [no-delay: true]]".
>This disables Nagle and in some situations can improve performance.
>Don't use it for high-volume streaming though. For more information on
>this and other "unexplainable" performance differences between
>platforms, ask the Samba developers. They could tell you some stories
>:-).
>
>The REBOL network adaptation layer does not vary much by platform, not
>enough to explain those differences. It is more likely that the
>performance differences are the result of a problem in the script which,
>together with high CPU use, interacts with differences in the paging and
>scheduling algorithms of different operating systems, leading to
>different performance. Other software which combine high CPU use with a
>lot of I/O, e.g. compilers, often show similar performance variations.
>
>>>SOme other news: Rebol seems to be inconsistent in its network behaviour. I
>>>tested on Linux 2.4.x libc6, but Petr runs on 2.2.16 and observes CPU eating.
>>>Shouldn't the same script run the same on all platforms?
>>>
>
>Yes, it should, for the same input. If there are indeed differences then
>chances are that the input to the script (perhaps its timing) is
>different, and the script might have a race condition that triggers the
>difference in behavior. Incorrectly handled errors (e.g. from ports
>being closed in different order due to different timing) could explain
>such problems.
>
>Also, AFAIK Maarten uses the (undocumented) async-modes field in ports
>to implement async i/o. That field was never intended for use by
>anyone outside RT (anyone other than me, actually), and incorrect
>use may very well lead to undefined behavior, or to behavior that varies
>by platform. The reason why its undocumented is because it is very
>tricky to use correctly, in particular if you want asynchronous behavior
>for all situations (accepting a connection, connecting, reading,
>writing). "CPU eating" can easily be explained by having async-modes
>in the wrong state for a port that is part of system/wait-list or the
>argument to 'wait. In particular watch out for errors created by the
>other end (e.g. a closed connection), and how they are handled. An
>error handler which is too "global", fails to properly clean up
>after a port error, and leaves such a port in wait-list with async-modes
>in a wrong state, could easily explain busy-looping.
>
>If you have reproducable performance differences on different platforms
>then the best way to track down the cause is to run tcpdump. That might
>also reveal the reason why reusing a TCP connection slows things down.
>In our experience reusing TCP connections significantly improves
>performance, and we make use of that in Express.
>
Holger, guru stuff. Very interesting. I ran ethereal packet monitor, but
saw nothing, just some strange packets sent to DNS server. You described
Rebol internals without describing them at all :-) The nicest part is
the port for Holger (tm) :-) It made my day ....
btw: is there any change in networking stuff in IOS already, in
comparison to View for e.g.? Or will we have to wait till 3.0?
-pekr-
