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From: Mulyadi Santosa <a_mulyadi@softhome.net>
Subject: Re: [Qemu-devel] qemu becomes unresponsive sometimes
Date: Sun, 28 Nov 2004 17:18:04 +0700
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To: qemu-devel@nongnu.org
Cc: Paul Jakma <paul@clubi.ie>

Hello Paul :-)

> In trying to debug this problem and try find vaguely wherein qemu the
> problem lies, I've observed that strace'ing the spinning qemu'ing
> will cause it to become responsive again.

First, let me ask for confirmation, do you run Qemu on Solaris or Linux host? 
If this is on solaris, maybe my whole assumption would be useless

> I've actually taken to running my more important qemu instances with
> a backgrounded strace attached, with strace output directed to
> /dev/null.

Running strace on binary only change one thing: on every syscall, it will be 
recorded as mentioned by ptrace behaviour. AFAIK, this recording will make 
the traced binary (in this case Qemu binary) halt on each syscall invocation 
and signal receive. (man strace and man ptrace). After that, the parent 
process (the shell which fork Qemu) will continue the execution of Qemu 
binary by sending signal

So, my suspicion, somehow Qemu is put into task_interruptible by host kernel 
(Linux?) no matter how much is the load. But, it is possible that it is not 
the whole Qemu that is unresponsive, maybe it is just the Qemu 
monitor/display that is put into "sleep"

What do you think ? Fabrice any comment? Maybe we need to force waking up the 
whole Qemu process (SDL output, monitor, VNC perhaps) everytime there is a 
"CPU" activity inside the guest kernel? 

regards

Mulyadi