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Message-ID: <53BD791F.6040807@acm.org>
Date: Wed, 09 Jul 2014 10:17:19 -0700
From: David Rothenberger <daveroth AT acm DOT org>
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To: cygwin AT cygwin DOT com
Subject: Re: Severe performance degradation of writev
References: <lpciht$pc5$1 AT ger DOT gmane DOT org> <20140707101049 DOT GI1803 AT calimero DOT vinschen DOT de> <20140707134137 DOT GK1803 AT calimero DOT vinschen DOT de> <53BD7161 DOT 5030209 AT acm DOT org> <20140709170321 DOT GA9946 AT calimero DOT vinschen DOT de>
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Reply-To: cygwin AT cygwin DOT com

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 AT vinschen DOT 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, I just tried a transfer and verified the checksum of the
transferred file. It worked fine.


-- 
David Rothenberger  ----  daveroth AT acm DOT org

Hempstone's Question:
        If you have to travel on the Titanic, why not go first class?

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