[Qemu-devel] Re: KVM call minutes for Feb 1

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/01/2011 11:03 AM, Jan Kiszka wrote:
> On 2011-02-01 17:53, Anthony Liguori wrote:
>    
>> On 02/01/2011 10:36 AM, Jan Kiszka wrote:
>>      
>>> On 2011-02-01 16:54, Chris Wright wrote:
>>>
>>>        
>>>> KVM upstream merge: status, plans, coordination
>>>> - Jan has a git tree, consolidating
>>>> - qemu-kvm io threading is still an issue
>>>> - Anthony wants to just merge
>>>>     - concerns with non-x86 arch and merge
>>>>     - concerns with big-bang patch merge and following stability
>>>> - post 0.14 conversion to glib mainloop, non-upstreamed qemu-kvm will be
>>>>     a problem if it's not there by then
>>>> - testing and nuances are still an issue (e.g. stefan berger's mmio read issue)
>>>> - qemu-kvm still evolving, needs to get sync'd or it will keep diverging
>>>> - 2 implementations of main init, cpu init, Jan has merged them into one
>>>>     - qemu-kvm-x86.c file that's only a few hundred lines
>>>> - review as one patch to see the fundamental difference
>>>>
>>>>          
>>> More precisely, my current work flow is to pick some function(s), e.g.
>>> kvm_cpu_exec/kvm_run, and start wondering "What needs to be done to
>>> upstream so that qemu-kvm could use that implementation?". If they
>>> differ, the reasons need to be understood and patched away, either by
>>> fixing/enhancing upstream or simplifying qemu-kvm. Once the upstream
>>> changes are merged back, a qemu-kvm patch is posted to switch to that
>>> version.
>>>
>>> Any help will be welcome, either via review of my subtle regressions or
>>> on resolving concrete differences.
>>>
>>> E.g. posix-aio-compat.c: Why does qemu-kvm differ here? If it's because
>>> of its own iothread code, can we wrap that away or do we need to
>>> consolidate the threading code first? Or do we need to fix something in
>>> upstream?
>>>
>>>        
>> I bet it's the eventfd thing.  It's arbitrary.  If you've got a small
>> diff post your series, I'd be happy to take a look at it and see what I
>> can explain.
>>
>>      
> Looks like it's around signalfd and its emulation:
>    

I really meant the compatfd thing.

signalfd can't really be emulated properly so in upstream we switched to 
a pipe() which Avi didn't like.

But with glib, this all goes away anyway so we should just drop the 
qemu-kvm changes and use the upstream version.  Once we enable I/O 
thread in qemu.git, we no longer need to use signals for I/O completion 
which I think everyone would agree is a better solution.

Regards,

Anthony Liguori