High Performance SSH/SCP - HPN-SSH when?

Corinna Vinschen vinschen at redhat.com
Thu Apr 13 00:43:38 EST 2006

On Apr 12 22:10, Darren Tucker wrote:
> On Wed, Apr 12, 2006 at 01:46:32PM +0200, Corinna Vinschen wrote:
> > Looks like another buffer might be in the way now, but I didn't look
> > into this deeper so far.
> Attached is a patch I started to play with that outputs the buffer
> high water mark for each connection.

Results for

  cygwin> scp linux:file .

1. Vanilla with 8K buffers:

  file  100%  118MB   1.3MB/s   01:35    
  buffer hiwater 1105968

2. Vanilla with 85K buffers:

  file  100%  118MB   5.6MB/s   00:21
  buffer hiwater 202176

3. HPN with 8K buffers:

  file  100%  118MB   1.0MB/s   02:00    
  buffer hiwater 1069056

4. HPN with 85K buffers:

  file  100%  118MB   9.9MB/s   00:12    
  buffer hiwater 1205576

Results for

  linux> scp file cygwin:

5. Vanilla sshd

  file  100%  118MB   9.1MB/s   00:13
  slave buffer hiwater 1085440

6. HPN sshd

  file  100%  118MB   2.0MB/s   00:58
  slave buffer hiwater 1085440

It's interesting that the buffer in case 4 is reproducibly only filled
up to 200K, while in all other cases the buffer is filled up to 1 Meg.
Is there anything we can learn from that?

> > Note that all tests are using a vanilla OpenSSH on the Linux side.
> > I didn't want to add another variable to the test configuration.
> Be aware that some of the hpn changes only kick in if it sees the other
> end is also hpn.

I am aware of that.  The idea is that I have only the Cygwin side under
control since that's what I'm maintaining.  The generic case is the one
in which I don't know anything about the remote side and can't influence


Corinna Vinschen
Cygwin Project Co-Leader
Red Hat

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