Mail Archives: cygwin/2009/07/01/05:26:44
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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