Re: Severe performance degradation of writev

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Jul  9 09:44, David Rothenberger wrote:
> Corinna Vinschen wrote:
> > On Jul  7 12:10, Corinna Vinschen wrote:
> >> On Jul  7 07:28, jojelino wrote:
> >>> 2008-07-27  Corinna Vinschen  <corinna@vinschen.de>
> >>> 
> >>> * fhandler_socket.cc (fhandler_socket::send_internal): Send
> >>> never more then 64K bytes at once.  For blocking sockets, loop
> >>> until entire data has been sent or an error occurs. 
> >>> (fhandler_socket::sendto): Drop code which sends on 64K bytes. 
> >>> (fhandler_socket::sendmsg): Ditto.
> >>> 
> >>> This commit added workaround for KB823764. but it has brought
> >>> another performance issue when writev sends <64k of data.
> >> 
> >> That's why the code contains that FIXME comment.  If you have a
> >> good idea for simple code to split a message into the least
> >> number of pieces to minimize the number of WsaSendTo calls...
> > 
> > I took a stab at the code and I think the new version improves
> > writing multiple small buffers a lot.  In my testing it still works
> > in other scenarios, too, but I would be very grateful if somebody
> > could have a critical look into my code changes as posted in 
> > https://cygwin.com/ml/cygwin-cvs/2014-q3/msg00003.html
> > 
> > I uploaded a new developer snapshot to
> > http://cygwin.com/snapshots/ Please give it a thorough try.
> 
> FWIW, this snapshot fixed a recent performance degradation for me when
> doing ssh/rsync transfers within my local network at work. These
> transfers had run at about 25 MB/s but recently degraded to about 500
> kB/s. The snapshot restored the original performance.

Cool.  Is the result still intact?  It's kind of simple to have
lots of performance if the code just doesn't send everything... :}


Corinna

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

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