Severe performance degradation of writev
Corinna Vinschen
corinna-cygwin@cygwin.com
Fri Jul 11 10:35:00 GMT 2014
On Jul 9 10:17, David Rothenberger wrote:
> Corinna Vinschen wrote:
> > 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... :}
>
> Details, details. :)
Yeah, yeah, I know, I'm nitpicking here ;)
> Yeah, I just tried a transfer and verified the checksum of the
> transferred file. It worked fine.
Thanks!
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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