Re: 2.6 vs 2.4, ssh terminal slowdown

From: Grant Coady
Date: Wed Feb 08 2006 - 00:37:19 EST

Hi Willy,
On Wed, 8 Feb 2006 06:17:09 +0100, Willy Tarreau <willy@xxxxxxxxx> wrote:

>Hi Grant,
>On Wed, Feb 08, 2006 at 03:51:24PM +1100, Grant Coady wrote:
>> On Wed, 8 Feb 2006 14:00:59 +1100, Con Kolivas <kernel@xxxxxxxxxxx> wrote:
>> >This is the terminal's fault. xterm et al use an algorithm to determine how
>> >fast your machine is and decide whether to jump scroll or smooth scroll. This
>> >algorithm is basically broken with the 2.6 scheduler and it decides to mostly
>> >smooth scroll.
>> Strange it does that over localnet to a PuTTY terminal on windoze.
>> Seems a strange thing to do in the kernel though, presentation
>> buffering / management surely can be done in userspace?
>I suspect the sshd on the firewall gets woken up for each line and it
>behaves exactly like an xterm. After having done a lot of "ls -l|cat"
>on 2.6, I'm not surprized at all :-/
>A good test would be to strace sshd under 2.4 and 2.6. You could even
>use strace -tt. Probably that you will see something like 1 ms between
>two reads on 2.6 and nearly nothing between them in 2.4.

Yes, it is nearly 1ms per line delay with 2.6, but 2.4 and 2.6 with the
trailing '|cat' give similar times, didn't try that notion last time.

We know now it isn't the network cards, disk I/O, just an oddness in 2.6 ;)

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