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Re: [Qemu-devel] Qemu-KVM 0.12.3 and Multipath -> Assertion

From: Kevin Wolf
Subject: Re: [Qemu-devel] Qemu-KVM 0.12.3 and Multipath -> Assertion
Date: Tue, 04 May 2010 16:01:35 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4

Am 04.05.2010 15:42, schrieb Peter Lieven:
> hi kevin,
> you did it *g*
> looks promising. applied this patched and was not able to reproduce yet :-)
> secure way to reproduce was to shut down all multipath paths, then 
> initiate i/o
> in the vm (e.g. start an application). of course, everything hangs at 
> this point.
> after reenabling one path, vm crashed. now it seems to behave correctly and
> just report an DMA timeout and continues normally afterwards.

Great, I'm going to submit it as a proper patch then.

Christoph, by now I'm pretty sure it's right, but can you have another
look if this is correct, anyway?

> can you imagine of any way preventing the vm to consume 100% cpu in
> that waiting state?
> my current approach is to run all vms with nice 1, which helped to keep the
> machine responsible if all vms (in my test case 64 on a box) have hanging
> i/o at the same time.

I don't have anything particular in mind, but you could just attach gdb
and get another backtrace while it consumes 100% CPU (you'll need to use
"thread apply all bt" to catch everything). Then we should see where
it's hanging.


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