Re: speed limitation with scp and sftp using openssh

On Fri, Feb 24, 2006 at 11:31:59AM -0600, cremes.devlist@xxxxxxx wrote:
Take a look at this [1] for an explanation. Last I heard these
patches were not accepted into the trunk because they didn't conform
to some style guidelines.

Corrections welcome...

Well, they didn't conform to the style guidelines (and there were other
issues[2] such as duplicated code and minor bugs, although those may have
been addressed by now) but that wasn't the main reason.

The main reason was that they're not right yet; they actually reduce
performance in some common cases (eg relatively fast networks and
slow hosts, up to 25% in my tests). It's still doing exactly the same
amount of work so there's no fundamental reason why this should be so.

People affected enough by the BDP to seek out the patch will gain back
the performance hit and more so for them the patch is a net win even with
those problems. For the general case it's not so clear-cut. See:
http://marc.theaimsgroup.com/?l=openssh-unix-dev&m=112884429502318
http://marc.theaimsgroup.com/?l=openssh-unix-dev&m=112886897105941

I've been trying to find some time to go back and look at this again
but haven't been able to yet.

[1] http://www.psc.edu/networking/projects/hpn-ssh/

[2] http://marc.theaimsgroup.com/?l=openssh-unix-dev&m=112316226728255

--
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69
Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.

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