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[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-