On 07/14/2011 04:00 PM, Sasha Levin wrote:
>
> Why? virtio is mature. It's not some early boot thing which fails and
> kills the guest. Even if you get an oops, usually the guest is still alive.
virtio is mature, /tools/kvm isn't :)
>
> > It's not just virtio which can fail running on virtio-console, it's also
> > the threadpool, the eventfd mechanism and even the PCI management
> > module. You can't really debug it if you can't depend on your debugging
> > mechanism to properly work.
>
> Wait, those are guest things, not host things.
Yes, as you said in the previous mail, both KVM and virtio are very
stable. /tools/kvm was the one who was being debugged most of the time.
I still don't follow. The guest oopses? dmesg | less. An issue with
tools/kvm? gdb -p `pgrep kvm`.
> > So far, serial is the simplest, most effective, and never-failing method
> > we had for working on guests, I don't see how we can work without it at
> > the moment.
>
> I really can't remember the last time I used the serial console for the
> guest. In the early early days, sure, but now?
>
I don't know, if it works fine why not use it when you need simple
serial connection?
It's also useful for kernel hackers who break early boot things :)
I'm not advocating removing it! I'm just questioning the need for
optimization.
> That's not what scaling means (not to say that it wouldn't be nice to
> fix coalesced mmio).
>
> btw, why are you so eager to run 1024 vcpu guests? usually, if you have
> a need for such large systems, you're really performance sensitive.
> It's not a good case for virtualization.
>
>
I may have went too far with 1024, I have only tested it on 254 vcpus so
far - I'll change that in my patch.
It's also not just a KVM issue. Take for example the RCU issue which we
were able to detect with /tools/kvm just by trying more than 30 vcpus
and noticing that RCU was broken with a recent kernel.
Testing the kernel on guests with large amount of vcpus or virtual
memory might prove beneficial not only for KVM itself.
Non-performance testing of really large guests is a valid use case, I agree.
--
error compiling committee.c: too many arguments to function
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