Re: [uml-user] bonnie++ almost hangs guest with UBD_SYNC=y.

[Jeff D. <jd...@ad...>]

bla...@ya... said:
> The IO is always synchronous. But in the better case it's performed by
> a  separate thread (which will wait for the IO to complete), while in
> the other  case it's performed by the main UML thread, which will wait
> for IO  completion, remaining idle meanwhile, while instead it could
> do anything else  (like letting another UML process run or perform
> tasks which don't require  those datas). In fact, I wrote a patch so
> using CONFIG_BLK_DEV_UBD_SYNC will  become like using ubd0s= ubd1s=...

This is just broken.  I have no idea how it got this way.  These are two
entirely different sorts of synchronous.  CONFIG_BLK_DEV_UBD_SYNC originally
did (O_SYNC or !O_SYNC) IO in process context rather than in the io_thread.  
ubd=sync or ubd*s do O_SYNC IO to the host.

I can't remember why CONFIG_BLK_DEV_UBD_SYNC was added, which is always a
bad sign.  Maybe it was a debugging crutch.  I think it should just be removed.

				Jeff