Re: Severe performance degradation of writev

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

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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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