Re: [PATCH 5/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_SOCKET

Anthony Liguori
2011-07-20T02:52:26Z

On 07/14/2011 08:23 AM, Avi Kivity wrote:
> On 07/14/2011 04:17 PM, Pekka Enberg wrote:
>> >
>> > I still don't follow. The guest oopses? dmesg | less. An issue with
>> > tools/kvm? gdb -p `pgrep kvm`.
>>
>> When I was debugging tools/kvm virtio code, I used to 'instrument' the
>> guest kernel with printk() calls which helped a lot.
>>
>
> Sure, but do you really need it spewing out the serial port all the time?
>
>> Also, a bug in tools/kvm can manifest in many interesting ways in the
>> guest kernel during boot, for example. You can't do dmesg then and gdb
>> won't save you. I think you've lived too long in the table KVM and Qemu
>> land to remember how important reliable printk() is for development.
>
> I guess. Also I've switched to trace_printk() since it's much nicer (and
> intergrates with other ftrace features).
>
> And again, I'm not against tools/kvm optimizing serial. I just want
> better justification for socket-mmio.

Just to be really thorough, the optimization is incorrect for UART
emulation. Maybe for a simple PIO based console where there were no
guest visible side effects to a character write, this would be okay, but
that is not how a UART works.

Just implement virtio-serial :-) You can move data as fast as you'd
like through it.

And if virtio-serial is too complicated, make a simpler version that
doesn't have such crazy semantics.

Regards,

Anthony Liguori

>