Re: [Qemu-devel] PPC: Timer issues with git master

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

On 11/10/13 09:44, Paolo Bonzini wrote:

>> I've just upgraded my git repository from around the 1.6 release
>> timeframe to git master and I'm seeing some strange timing issues
>> running through my OpenBIOS test suite which weren't there before my git
>> update.
>>
>> The two most noticeable changes are in FreeBSD and HelenOS; the
>> countdown timer in the FreeBSD bootloader used to count down in seconds
>> whereas now it whizzes down to zero, and HelenOS now takes a very very
>> long time to boot.
>>
>> In order to reproduce from git master download the appropriate ISOs and
>> launch QEMU like this:
>>
>> ./qemu-system-ppc -cdrom
>> /home/build/src/qemu/image/ppc/FreeBSD-9.1-RC2-powerpc-release.iso -M
>> mac99 -m 512 -boot d
>>
>> ./qemu-system-ppc -cdrom
>> /home/build/src/qemu/image/ppc/HelenOS-0.4.2-ppc32.iso -m 512 -boot d
>>
>> Paulo/Alex B - I know you've been working with timers, so wondered if
>> this is related to some of the changes you've been making? I've also
>> copied Alex Graf in case this is somehow related to how the timer code
>> interacts with the PPC timebase-frequency.
>
> Can you bisect them?
>
> Paolo

Hi Paolo,

I've just attempted a bisection testing HelenOS, but I'm struggling to 
get a consistent result. Even with the same binary across multiple runs 
then sometimes I see the issue with frequent timer pauses, and sometimes 
I don't which makes tracking this down very difficult.

What I do see post-timer-rework is that when it does occur, the screen 
redraws become really really slow; rectangular blocks (maybe 2 per sec 
or so?) are redrawn very slowly working their way down the screen. I 
have a feeling from memory that HelenOS does tend to hit the timer 
interrupts quite hard on PPC so could it be that the new code somehow 
blocks screen updates under high timer interrupt load?

As for the FreeBSD issue, this seems to be something different from the 
HelenOS issue and I see it even with QEMU 1.6. A quick browse around the 
git logs points me towards this as a possible suspect: 
http://git.qemu.org/?p=qemu.git;a=commit;h=a0f9fdfd98cc0571f9921a7eadd7316532e3e289.


ATB,

Mark.