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Re: [Qemu-devel] [PATCH] hid: Extend the event queue size to 1024

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [PATCH] hid: Extend the event queue size to 1024
Date: Thu, 14 Apr 2016 18:19:01 +0200

On Do, 2016-04-14 at 17:29 +0200, Alexander Graf wrote:
> On 04/14/2016 05:17 PM, Gerd Hoffmann wrote:
> > On Do, 2016-04-14 at 16:25 +0200, Alexander Graf wrote:
> >> We can currently buffer up to 16 events in our event queue for input
> >> devices. While it sounds like 16 events backlog for everyone should
> >> be enough, our automated testing tools (OpenQA) manage to easily
> >> type faster than our guests can handle.
> > IMO you should fix OpenQA to type slower then.
> >
> > Real hardware is made for human typing speeds.  qemu emulates real
> > hardware.  Typing insane fast is going to cause problems because the
> > hardware interfaces are not designed for that.
> >
> > Note the ps/2 keyboard has only a 16 byte queue too.  Used to be 256
> > bytes, but that caused problems because this diverges from real hardware
> > (see commit 2858ab09e6f708e381fc1a1cc87e747a690c4884 for all the
> > details).
> >
> > Note that the generic input code has support for slow typing already
> > (see qemu_input_event_send_key_delay in ui/input.c).  That queue will
> > (a) work for all keyboard devices and (b) isn't visible to the guest, so
> > using that might be a reasonable option if you can't put the delay logic
> > into OpenQA.  How to you feed the guest with keystrokes?  monitor?  vnc?
> It used to type via the monitor, but these days everything goes via vnc.
> Vnc already uses qemu_input_event_send_key_delay today, so I'm not sure 
> where things fall apart.

Try a larger delay for starters.

Possibly OpenQA starts typing before the guest detected the device, in
that case the delay wouldn't avoid the queue filling up because the
guest doesn't read it (yet).


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