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Re: Slow Upload Performance on High-Bandwidth connections on windows

From: Christian Hägele <>
Date: Tue, 5 Feb 2013 20:17:27 +0000 (UTC)

Thank you for your input. That rules out some misconfiguration in windows.

In my opinion CURL_MAX_WRITE_SIZE should not have a big effect on the speed,
because the TCP-stack shouldn't care in what chunks the application wants to send
data over the TCP-connection. It can have an effect if the application doesn't
fill up the TCP-buffer fast enough, though.

So i have 2 questions as follow up:

1. In the bug-report you said you are seeing upload-speeds of ~500KiB/s with
curl and up to 6MiB/s with FileZilla. The other numbers you provided recently
where somewhere around 18MiB/s. So I suppose you did not test the linux ftp
server in another country? What where your test-setup for your recent numbers?
Especially the latency (round-trip-time) between the two peers is very
important here.

2. Did you try keep the CURL_MAX_WRITE_SIZE at default and try to increase the
SO_SNDBUF option manually to a very large value (e.g. 8MiB)?

I have the assumption that in your latest tests the limiting factor was not the
TCP-connection but the CPU in pumping the data fast enough to the TCP-stack. If
that is the case then that is another issue.



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Received on 2013-02-05