cURL / Mailing Lists / curl-library / Single Mail


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

From: Kurushin Andrey <>
Date: Wed, 6 Feb 2013 15:07:01 +0400

1. the main bug report (filezilla vs far manager vs curl) contains test of cross-countries
test results (ping >8ms). recent tests (with custom builds of 7.28.1) were made inside single subnet (ping < 1ms) so they have better speed values.

2. CURL_MAX_WRITE_SIZE = 16kb and SO_SNDBUF=8mb gives very good ftp upload speed (equal to version with big global buffer), but sftp upload speed still have 6Mb/s limit.
So the best way to increase both ftp and sftp upload speed is to increase CURL_MAX_WRITE_SIZE;
I understand that sftp limit may have different nature - but now it's also depends on CURL_MAX_WRITE_SIZE value.

06.02.2013, в 0:17, Christian Hägele <> написал(а):

> 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.
> Regards,
> Christian
> -------------------------------------------------------------------
> List admin:
> Etiquette:

List admin:
Received on 2013-02-06