Severe performance degradation of writev

Wed Jul 9 16:46:00 GMT 2014

Corinna Vinschen wrote:
> On Jul 7 12:10, Corinna Vinschen wrote:
>> On Jul 7 07:28, jojelino wrote:
>>> 2008年07月27日 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.
-- 
David Rothenberger ---- daveroth@acm.org
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 The Path of Progress:
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