On Sun, 15 Mar 2009, Daniel Stenberg wrote:
> Right now I'm at 20MB/s speed for SCP downloads but this code has some minor
> regression still that I need to fix before I can commit. SFTP is at 12MB/s.
It's really all about the channel window handling, and when we're talking raw
localhost transfers we clearly need to set a very large window to get close to
top speed for SCP.
I've simplified the libssh2_channel_read_ex() function a lot and now we send
the window adjust package less frequent.
I've also right now made the window adjust logic like this:
if (window size < LIBSSH2_CHANNEL_WINDOW_DEFAULT*100 )
set window size = LIBSSH2_CHANNEL_WINDOW_DEFAULT*200
Yes, 100 and 200! LIBSSH2_CHANNEL_WINDOW_DEFAULT is 64K so you can see how
this is a pretty big window. This way, I can repeatedly transfer my 1GB file
over SCP at 38MB/s! (SFTP still left at only almost 14MB/s).
If I do the logic with *10 and *20 window instead, I don't get more than
~25MB/s! If I use *300 and *600 I in fact get close to 40MB/s. Which happens
to be the openssh speed. I must confess this makes me pretty content.
Can anyone think of any particular downside with going with these rather
extreme window sizes as-is, or should we work on getting a more clever scheme
for them?
--
/ daniel.haxx.se
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