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Date: Fri, 11 Jul 2014 12:35:40 +0200
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: Severe performance degradation of writev
Message-ID: <20140711103540.GA18114@calimero.vinschen.de>
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References: <lpciht$pc5$1@ger.gmane.org> <20140707101049.GI1803@calimero.vinschen.de> <20140707134137.GK1803@calimero.vinschen.de> <53BD7161.5030209@acm.org> <20140709170321.GA9946@calimero.vinschen.de> <53BD791F.6040807@acm.org>
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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>
> >>>>>=20
> >>>>> * 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.
> >>>>>=20
> >>>>> This commit added workaround for KB823764. but it has
> >>>>> brought another performance issue when writev sends <64k of
> >>>>> data.
> >>>>=20
> >>>> 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...
> >>>=20
> >>> I took a stab at the code and I think the new version improves=20
> >>> 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=20
> >>> https://cygwin.com/ml/cygwin-cvs/2014-q3/msg00003.html
> >>>=20
> >>> I uploaded a new developer snapshot to=20
> >>> http://cygwin.com/snapshots/ Please give it a thorough try.
> >>=20
> >> 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.
> >=20
> > Cool.  Is the result still intact?  It's kind of simple to have=20
> > lots of performance if the code just doesn't send everything... :}
>=20
> 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

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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