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From: "Steven Hartland" <killing AT multiplay DOT co DOT uk>
To: <cygwin AT cygwin DOT com>
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Subject: Re: socket performance (was Re: Building cygwin1.dll)
Date: Tue, 10 Jan 2012 15:24:41 -0000
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If your running Windows 7 or 2k8 are you running the following hotfix, if not
you should try that too, just in case you machine has got a degraded tcp
stack.

http://support.microsoft.com/kb/983528

    Regards
    Steve

----- Original Message ----- 
From: "Corinna Vinschen"
Sent: Tuesday, January 10, 2012 2:45 PM
Subject: Re: socket performance (was Re: Building cygwin1.dll)


> On Jan 10 14:45, Johan van den Berg wrote:
>>
>> On 09 Jan 2012, at 3:43 PM, Corinna Vinschen wrote:
>>
>> > How's the performance in your scenario when applying the below patch
>> > instead of yours?
>>
>> I have to run back with my tails between my legs. I implemented your patch, and the transfer speed on a 200ms latency, 10mbit 
>> max link went down to 5-6mbit using rsync. I then rolled back to my version, and suddenly also got 5-6mbit. I started another 
>> rsync and I was able to max the 10mbit line, hence, I think my original patch never had the effect I hoped for.
>>
>> Checking further, I noticed that stopping a task in windows task scheduler doesn't actually stop the rsync, so the only reason 
>> why I then must have seen that 10mbit max on my patch was simply because another rsync was already running ;(
>>
>> I am now however back to the drawing board. With your patch on both ends of the line, with a client rsync option of 
>> "--sockopts=SO_SNDBUF=2000000,SO_RCVBUF=2000000" I still only get 5-6mbit max. I installed iperf on both ends, and no 
>> combination of settings (higher window size, higher MSS) will give me more than 5-6mbit transfer rate, except when I add the -P 
>> option which does parallel transfers. As soon as I do parallel, I can max the line. I then tested with a 100mbit link, and got 
>> similar results.
>>
>> Thinking outside the box, I started up iperf on a linux box on the other end of a 100mbit line:
>>
>> Cygwin to cygwin = 5mbit
>> Cygwin to linux = 5mbit
>> Linux to linux = 28mbit
>>
>> In all cases, adjusting the window size had no effect other than making the client "think" it can transfer faster if the buffer 
>> is bigger than the total amount of data to send.
>>
>> Any advice while I carry on trying to figure this out?
>
> What Windows versions are we talking about?  Is that pre-Vista?  XP,
> for instance?  If so, setting the buffer size > 64K should have no effect.
>
> I really don't know why the performance should be so much worse than
> under Linux in your scenario, sorry.  Cygwin is not trying to do
> anything fancy.  The speed should be basically in the same range as on
> Linux.
>
> At least it is for me when using sftp.  When using scp I just found that
> I get a similar bad performance, only 6.9 MB/s instead of 35 MB/s.
>
> Is it possible that the limiting factor is not the socket, but the pipes
> between rsync and ssh, assuming you are using rsync over ssh?
>
>
> Corinna
>
> -- 
> Corinna Vinschen                  Please, send mails regarding Cygwin to
> Cygwin Project Co-Leader          cygwin AT cygwin DOT com
> Red Hat
>
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