Am 02.08.2011 16:23, schrieb Avi Kivity: > On 07/26/2011 02:48 PM, Kevin Wolf wrote: >> Depends on Stefan's latest coroutine patches. This series makes qcow and >> qcow2 >> take advantage of the new coroutine infrastructure. Both formats used >> synchronous operations for accessing their metadata and blocked the guest CPU >> during that time. With coroutines, the I/O will happen asynchronously in the >> background and the CPU won't be blocked any more. >> > > Do you plan to convert qcow2 to a fully synchronous design? > > IMO that will make it more maintainable. Cancellation will need some > thought, though.
After this patch series, all interesting paths are free of callbacks (I assume this is what you mean by synchronous?). The only thing I can see that is left is qcow2_aio_flush. What is required are some cleanups that eliminate things that still look like AIO code, and yes, that's something that I want to have. Frediano has posted some patches which I haven't fully reviewed yet, but the qcow1 RFC he posted was definitely a step in the right direction. Regarding cancellation, I don't know any driver that really does what it's supposed to do. There are basically two ways of implementing it in current code: Either by completing the request instead of cancelling, or it's broken. I'd suggest that we implement waiting for completion as a generic function in the block layer and be done with it (actually this is what happens with bdrv_aio_co_cancel_em, it just could be a bit finer grained). Kevin
