Re: [Qemu-devel] [PATCH 1.1] coroutine: Avoid ucontext usage on i386 Linux host

[Anthony Liguori <aliguori@us.ibm.com>]

On 05/09/2012 04:27 PM, Peter Maydell wrote:
> On 9 May 2012 21:59, Anthony Liguori<aliguori@us.ibm.com>  wrote:
>> On 05/09/2012 03:46 PM, Peter Maydell wrote:
>>> Longer term (ie post 1.1) I'm strongly in favour of kicking
>>> out coroutines, because I think there clearly is no single
>>> solid portable implementation possible. C just isn't designed
>>> to allow them; better not to try to swim against the current.
>
>> Unfortunately, voting for code to be different doesn't actually make it
>> different.
>
> Yeah, I agree with this sentiment...
>
>> If you're volunteering to rewrite the block layer to not require coroutines
>> (either by using a state machine or by using re-entrant threads and fixing
>> any locking issues associated with that) that's wonderful.
>>
>> But we decided to not do synchronous I/O years ago and still haven't removed
>> it all from the tree.  Coroutines got us much closer to getting rid of
>> synchronous I/O.
>
> ...but I would at least like us to take the position that we don't
> introduce *more* users of coroutines.

I think the long term plan has been:

1) replace synchronous I/O users with coroutines + async I/O

2) promote coroutines to threads by introducing fine grain locking.

I don't think avoiding coroutines helps us along this route nor does it help 
eliminate immediate users of coroutines.

I think our best strategy forward is to get rid of async I/O in the blocker 
layer and in devices.  Then I think we should promote coroutines as much as 
possible.

Regards,

Anthony Liguori

>
> -- PMM
>