Severe performance degradation of writev
Corinna Vinschen
corinna-cygwin@cygwin.com
Wed Jul 9 17:03:00 GMT 2014
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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