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

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

On 17/10/13 15:53, Paolo Bonzini wrote:

>> 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.
>
> Can you try reverting this on top of git master (and test both guests)?

I've tried it with FreeBSD and it doesn't make any difference; the fix 
doesn't matter for the HelenOS regression as that timer is only setup 
for -M mac99.

To summarise what I've found today with HelenOS: I see failures with 
both 1.6 and git master, but git master appears to be a lot worse in 
terms of triggering the problem.

Also with git master, I see time periods where the timer speeds up for a 
couple of seconds at a time (as apparent by the HelenOS circling orbs) 
and then slows back down again. And the keyboard (whilst sluggish under 
1.6) is very unresponsive under git master.

I'm starting to wonder like Alex B if these changes have made an already 
existing bug more apparent.


ATB,

Mark.