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Date: Tue, 30 Jun 2009 13:26:17 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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Subject: Re: Call for TESTING (was Re: [1.7.0-50] scp progress counter 	flies   through first 175 MB or so)
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On Jun 29 12:59, Warren Young wrote:
> I scp'd a 1.6 GB file back and forth to a Linux server over GigE to a  
> fast new RAID-10.  I tested 1.7.0-50 and 20090629.
>
> Results:
>
> On a 32-bit XP box, 1.7.0-50 gives about 15 MByte/sec for both upload  
> and download.  (This box can't really hit GigE speeds due to crappy  
> cabling and a low-quality switch.)  On switching to the snapshot, the  
> download speed is about the same, but upload is cut to 4-5 MB/sec.
>
> On a 64-bit Vista box, 1.7.0-50 gives inconsistent behavior.  Download  
> behaves as it should: ~45 MB/sec here, due to better switch and cabling.  
>  But, uploading with scp gives the reported behavior: the scp status  
> fills out to 100% very fast but then scp doesn't finish running for  
> quite a while.  It's like it's buffering a big fraction of the 1.6 GB,  
> which isn't impossible, since this box has 12 GB of RAM.  (Core i7,  
> DDR3, wheee!)
>
> After switching to the snapshot on that Vista-64 box, the scp progress  
> display becomes useful, growing steadily as scp runs.  Unfortunately, my  
> upload speed is down to around 5 MB/sec here, just as on the XP box.
>
> A different non-Cygwin scp client I have here can manage much faster  
> transfer speeds, so I can rule out disk and network bottlenecks.  The  
> slowdowns are in Cygwin itself or the Cygwin scp port.
>
> I can rule out a problem in the general network I/O handling: changing  
> the DLL doesn't seem to affect ttcp results materially.  It's either scp  
> or the way scp uses cygwin1.dll.

I just had a look into this and I think I found a way to raise the
outbound transfer rates somewhat.  The outbound speed is always slower
than the inbound speed, no matter what I try.  However, I'm now at a
point where it might be more acceptable.

One of my test machines, a 2K8 32 bit box has the following scp
transfer rates under 1.5.25:

  inbound:  17.2 MB/s
  outbound:  3.5 MB/s

With the latest snapshot:

  inbound:  21.5 MB/s
  outbound:  4.2 MB/s

With the latest from CVS:

  inbound:  21.5 MB/s
  outbound: 11.5 MB/s

What's still not clear is why the ssh process takes so much CPU.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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