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Re: Call for TESTING (was Re: [1.7.0-50] scp progress counter flies through first 175 MB or so)
- From: Corinna Vinschen <corinna-cygwin at cygwin dot com>
- To: cygwin at cygwin dot com
- Date: Wed, 1 Jul 2009 11:26:17 +0200
- Subject: Re: Call for TESTING (was Re: [1.7.0-50] scp progress counter flies through first 175 MB or so)
- References: <20090625145005.GB18338@ednor.casa.cgf.cx> <20090628193155.GA10407@ednor.casa.cgf.cx> <20090629092857.GZ30864@calimero.vinschen.de> <20090629095322.GD30864@calimero.vinschen.de> <20090629142348.GB19123@ednor.casa.cgf.cx> <20090629144030.GC19123@ednor.casa.cgf.cx> <4A490F0E.6040806@etr-usa.com> <20090630112617.GS30864@calimero.vinschen.de> <4A4A3B64.4030004@etr-usa.com> <Pine.CYG.4.58.0906301407590.4092@PC1163-8460-XP.flightsafety.com>
- Reply-to: cygwin at cygwin dot com
On Jun 30 14:23, Brian Ford wrote:
> 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.
The data is copied only once, from the application buffer to the
underlying WinSock socket buffer and vice versa. There's no additional
copy of buffer data in Cygwin.
> 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 removed the sig_dispatch_pending calls from send/recv and friends.
Note, however, that this has no influence on the ssh/scp results we were
talking about in this thread. ssh/scp are using read/write calls.
Anyway, using ssh/scp with the latest from CVS looks much better now.
It doesn't eat up all CPU anymore and the performance looks pretty
well as far as I can tell.
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
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