Weird delay on long command lines

Weird delay on long command lines

[Mikael Magnusson]

This mostly happens when i paste gcc commands from autoconf, but it's
easy to reproduce with the alt-number keybinds. For example type
alt-1000 and press a, then press left arrow. You'll notice it takes a
second or two before anything happens. I've confirmed the same thing
happens with zsh -f. Attaching with strace shows the final argument to
poll() seems to be O(n) with the command line length but I really have
no idea why (or what the poll is for, haven't looked at the code).

--
Mikael Magnusson

Re: Weird delay on long command lines

[Peter Stephenson]

Mikael Magnusson <mikachu@gmail.com> wrote:
> This mostly happens when i paste gcc commands from autoconf, but it's
> easy to reproduce with the alt-number keybinds. For example type
> alt-1000 and press a, then press left arrow. You'll notice it takes a
> second or two before anything happens. I've confirmed the same thing
> happens with zsh -f. Attaching with strace shows the final argument to
> poll() seems to be O(n) with the command line length but I really have
> no idea why (or what the poll is for, haven't looked at the code).

It's to do with the optimisation of the display for low baud rates.  BAUD is
initiliased from the terminal driver which may well have it set to
something low like 38400.  Try setting it to something much larger, or
unsetting BAUD altogether.

It's probably more trouble than it's worth nowadays; the number of serial
line terminals, or even remote terminals where it's worth optimising the
terminal handling, is probably quite limited.  Maybe it shouldn't be set by
default.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070


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Re: Weird delay on long command lines

[Mikael Magnusson]

On 12/12/05, Peter Stephenson <pws@csr.com> wrote:
> Mikael Magnusson <mikachu@gmail.com> wrote:
> > This mostly happens when i paste gcc commands from autoconf, but it's
> > easy to reproduce with the alt-number keybinds. For example type
> > alt-1000 and press a, then press left arrow. You'll notice it takes a
> > second or two before anything happens. I've confirmed the same thing
> > happens with zsh -f. Attaching with strace shows the final argument to
> > poll() seems to be O(n) with the command line length but I really have
> > no idea why (or what the poll is for, haven't looked at the code).
>
> It's to do with the optimisation of the display for low baud rates.  BAUD is
> initiliased from the terminal driver which may well have it set to
> something low like 38400.  Try setting it to something much larger, or
> unsetting BAUD altogether.
>
> It's probably more trouble than it's worth nowadays; the number of serial
> line terminals, or even remote terminals where it's worth optimising the
> terminal handling, is probably quite limited.  Maybe it shouldn't be set by
> default.

Yeah, unsetting BAUD fixed it, thanks.

--
Mikael Magnusson