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SubjectRe: [patch] CFS scheduler, -v18

* Keith Packard <keith.packard@intel.com> wrote:

> On Tue, 2007-07-03 at 09:22 +0200, Ingo Molnar wrote:
>
> > which allows xterm-spam (attached) to easily flood the xterm
> > (without any scrolling that would act as a throttle) and the xterm
> > to flood Xorg.
>
> It's just an Xterm bug.
>
> Xterm will look for X input if it ever manages to fill the input
> buffer past 32768 bytes. If it manages to get more than 4096 bytes in
> one read, it will invoke sched_yield. and then check for input. Gotta
> love that sched_yield call.
>
> As it always processes all of the incoming data before trying to read
> again, there doesn't appear to be any way it can ever have more than
> 32768 characters in the buffer.
>
> And, as the kernel will not buffer more than 4095 bytes from a pty,
> there isn't any way it will ever read 4096 bytes.
>
> So, it sits there carefully reading every byte from the pty and
> painting them on the screen.

ah. Thanks for the explanation!

> You can 'fix' xterm with:
>
> $ xterm -xrm '*minBufSize: 4095'

indeed, that solves the xterm-spam Ctrl-C/Ctrl-Z problem here!

> I hesitate to even suggest a patch to xterm that would solve this
> problem correctly. Note that xterm has kludges in several of the
> output processing steps which explicitly look for input (most vertical
> cursor motion, it seems), which is why any application which scrolls
> doesn't cause this problem.
>
> Do you need more reasons to switch to another terminal emulator?
> gnome-terminal has finally gotten reasonable; I expect rxvt or konsole
> would work just as well.

yeah, i use gnome-terminal exclusively. But testers looking for CFS
regressions do run every shell on the planet :-)

gnome-terminal is also faster all around (at least on my box):

$ (echo '#!/bin/bash' ; echo 'for ((i=0; i<100000; i++)); do echo $i; done') > 1.sh; chmod +x 1.sh; time xterm $HOME/1.sh; time gnome-terminal -x ./1.sh

real 0m3.193s
user 0m2.840s
sys 0m0.460s

real 0m2.495s
user 0m2.430s
sys 0m1.520s

Ingo
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