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


From: Mark Cave-Ayland
Subject: Re: [Qemu-devel] PPC: Timer issues with git master
Date: Thu, 17 Oct 2013 16:16:22 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130116 Icedove/10.0.12

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.



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