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Re: [Qemu-devel] [BUG] GTK terminal is broken

From: Anthony Liguori
Subject: Re: [Qemu-devel] [BUG] GTK terminal is broken
Date: Mon, 29 Jul 2013 16:09:26 -0500
User-agent: Notmuch/0.15.2+202~g0c4b8aa (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu)

Stefan Weil <address@hidden> writes:

> Am 29.07.2013 22:34, schrieb Andreas Färber:
>> Am 29.07.2013 21:27, schrieb Stefan Weil:
>>> Am 29.07.2013 20:55, schrieb Anthony Liguori:
>>>> Stefan Weil <address@hidden> writes:
>>>>> Am 29.07.2013 20:05, schrieb Anthony Liguori:
>>>>>> Stefan Weil <address@hidden> writes:
>>>>>>> Hello,
>>>>>>> maybe most developers will already have noticed that the terminal output
>>>>>>> in QEMU's GTK user interface is broken. As far as I know, it never 
>>>>>>> worked,
>>>>>>> but as there are working alternatives, I did not care much and forgot to
>>>>>>> report the issues.
>>>>>>> See these snapshots which show the problems with QEMU's GTK terminals:
>>>>>>> http://qemu.weilnetz.de/test/bugs/qemu-gtk-demo1.png
>>>>>>> Here the first line of the QEMUmonitor is only partially visible.
>>>>>>> Tested with Cygwin/X on W64 host, QEMU running on Debian Linux.
>>>>>>> Other X servers (e.g. native X on Debian Linux) don't show this
>>>>>>> problem.
>>>>>> It's a GTK/Cygwin/X bug.
>>>>>> We use a vbox without anything particularly fancy happening.  Looks like
>>>>>> something is calculating layout incorrectly.
>>>>>> Regards,
>>>>>> Anthony Liguori
>>>>> I miss a comment on the more important next two points.
>>>>> They are _not_ related to Cygwin / X.
>>>>> Do you investigate them?
>>>> What you're seeing has always existed and is not GTK specific.  There is
>>>> not flow control on the outgoing side of serial emulation.  Data will
>>>> get dropped.
>>>> My guess is that your system is sufficiently slow and overloaded that
>>>> it's happening a lot for you.
>>>> Regards,
>>>> Anthony Liguori
>>> If it were as simply as that, that would be fine, but alas,
>>> it isn't. Even fast servers without any load show dropped
>>> characters. There are dropped characters for QEMU's
>>> monitor window (Alt-ctrl-2) and for Malta's line display
>>> (Alt-Ctrl-5). Neither of these two should suffer from missing
>>> flow control.
>>> And even a current X.Org on Ubuntu shows the first bug
>>> (crippled first line) here, so it is not Cygwin / X specific.
>> FWIW I've been seeing similar garbled-Gtk-output issues on openSUSE 12.3
>> but didn't investigate further. -monitor stdio has so far not failed me
>> on the same system by comparison.
>> One reproducible test case was the openrisc kernel that Jia provided
>> recently.
>> Regards,
>> Andreas
> Maybe the problems only occur with TCG, but not with KVM.
> That might explain why I get them more often than Anthony :-)
> Up to now, I did not try GTK terminals with KVM because my
> typical test scenario uses MIPS or ARM boards on Intel hosts.

x86 vs. other will come into play too.

The serial driver for x86 has some basic backoff logic.  I suspect
others don't.

My guess why you don't see this on -serial stdio is that it probably is
using synchronous I/O.


Anthony Liguori

> Regards,
> Stefan

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