Re: [Qemu-devel] Significant performance regression in qemu-system-mips.

[Aurelien Jarno <aurelien@aurel32.net>]

On Wed, Mar 24, 2010 at 03:34:00PM -0500, Rob Landley wrote:
> I have a native build under qemu that gets killed if it doesn't produce a line 
> of output for 60 seconds (hang detection enforced by the host monitoring 
> qemu's stdout with --nographic, not from within qemu).
> 
> In the most recent release version, it never came close to triggering on mips 
> with a 30 second timeout.  In the current -git version (well, as of Thursday 
> anyway), it triggers frequently (about 90% of the time) even with a 60 second 
> timeout.
> 
> I bisected it to this:
> 
> commit 1828be316f6637d43dd4c4f5f32925b17fb8107f
> Author: Paolo Bonzini <pbonzini@redhat.com>
> Date:   Wed Mar 10 11:38:41 2010 +0100
> 
>     more alarm timer cleanup
>     
>     The timer_alarm_pending variable is related to the alarm timer but not
>     placed in the struct.  Also, in qemu_mod_timer the wrong flag was being
>     tested: the timer is rearmed in the alarm timer "bottom half", so the
>     right flag to test there is the "pending" flag.
>     
>     Finally, I hoisted the NULL checks from alarm_has_dynticks to
>     host_alarm_handler.
>     
>     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>     Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> 
> Reverting that patch fixed it (git show HEAD | patch -R -p1), by which I mean 
> three consecutive runs with 30 second timeout didn't trigger the hang 
> detection.
> 

I have tried to reproduce the issue by measuring the boot time of a mips
system, but it stay unchanged between before and after the patch. Do you
have some more details about how to reproduce the issue ? Have you tried
to pay with the -clock option?

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net