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Date:	Tue, 30 Jun 2009 14:23:41 -0500
From:	Brian Ford <Brian DOT Ford AT FlightSafety 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 Tue, 30 Jun 2009, Warren Young wrote:

> Corinna Vinschen wrote:
> > What's still not clear is why the ssh process takes so much CPU.
>
> Too many buffer copies?  It takes a surprising amount of CPU power to
> fill a gigabit pipe from userland.  Double or triple that workload with
> unnecessary copies, and there goes your transfer rate, evaporating on
> the wind.

Even more so for context switches ;-):

http://www.cygwin.com/ml/cygwin-developers/2007-10/msg00040.html

although this performance penalty was removed from read/write and friends:

http://www.cygwin.com/ml/cygwin-developers/2007-12/msg00004.html

it is still present for send/recv and friends.

I'd be happy to make a donation or organize a fund raising effort if it
would help to find a work around for this long standing performance issue.

-- 
Brian Ford
Staff Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained crew...

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