Re: Network compatibility and performance

From: linux-os (Dick Johnson)
Date: Tue Aug 15 2006 - 07:31:47 EST

On Mon, 14 Aug 2006, Ben Greear wrote:

> linux-os (Dick Johnson) wrote:
>> No it will return FAIL (-1) or an error and 0 (the bottom of the procedure)
>> if the whole things went. It is mandatory that the whole thing goes
>> so this procedure should handle any intermediate actions.
> I see..I missed that part.
>> Upon your advice, I may try to add select() although, on a write it
>> seems to be putting in user-space something that used to be handled
>> quite well in the kernel. I don't think the user should really care
>> about the kernel internals, whether or not the kernel happens to have
>> a buffer available.
> Since you put it in non-blocking mode, you need the select() to throttle
> unless you want to busy spin. Whether you should have to actually put
> in in non-blocking mode or not is a different question.
>>> I have no idea why you need to add the MIN() logic..and that seems like
>>> something that should not be required.
>> It seems that some code 'thinks' that a large buffer of data is
>> an error and won't even try to send some anymore.
> I have seen a problem where I can repeatedly hang a TCP connection
> when running at high speed. The tx queue is full or mostly full, and
> on the wire I only see 200kpps of duplicate acks. Can't reproduce it
> with anything other than my big complicated proprietary app, so it
> remains unfixed.
> I am not sure if this is related to what you see or not..but could you
> check to see if there is lots of acks on the wire when this hang happens?

I will check to see what it's doing on the wire and get back.

>>> Even 112kbps sucks on a decent network. What is the speed of your
>>> network, what protocol are you using, if tcp, what is the latency
>>> of your network?
>> The network is a single wire about 8 feet long, connecting Intel gigibit
>> links on two identical computers (crossover cable). This link is TCP.
>> For high-speed data, I use UDP and I get a higher throughput because
>> there is no handshake. Thew latency is the latency of Linux. BTW, it's
>> only a gigaBIT link, you can divide that by 8 for gigabytes. I don't
>> know the actual bit-rate on the wires, if we assume 1GHz, the byte-rate
>> is only 125,000 bytes per second. Being able to use 89.6 percent of
>> that isn't bad at all.
> You must be meaning to add a few more zeros to that number. If you
> are getting ~125,000,000 Bytes per second then you are doing OK.

ACK that!

> Ben

Dick Johnson
Penguin : Linux version on an i686 machine (5592.62 BogoMips).
New book:

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