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Re: [Qemu-devel] [PULL 5/8] target-sparc: Use global registers for the r

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PULL 5/8] target-sparc: Use global registers for the register window
Date: Fri, 24 Jun 2016 08:36:31 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

On 24/06/2016 05:57, Richard Henderson wrote:
> Whatever happens, it happens after 10GB of logs, which is simply too
> much to sift through.  I've tried to narrow it down, but the lack of a
> hardware tlb refill means that we get hundreds of thousands of Data
> Access Faults that are simply TLB misses and not the actual Segmentation
> Fault in question.
> It doesn't seem to affect other OSes, so I can't imagine what quirk is
> being exercised in this case.
> As loath as I am to suggest it, we may have to revert the sparc indirect
> register patch for the release.

We have more than a month.  If it's reproducible, it can be fixed. :)

> I do now ping the rest of my sparc improvements patchset.  It's
> completely independent of the use of indirect registers.

Mark, perhaps you can try to use migration to reduce the amount of
logging?  (Start QEMU with -snapshot, try to stop the vm before it
fails.  If you succeed, do a "migrate exec:cat>foo.sav" followed by
"commit"; if you fail, try again).

It would be nice to have a mechanism to stop the VM after executing N
basic blocks.  Binary search on this value then can help with coming up
with a more easily debuggable snapshot, possibly to a point where the
difference between pre-patch and post-patch becomes deterministic.


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