Re: [Qemu-block] [Qemu-devel] [PATCH] aio-posix: honor is_external in AioContext polling

[Fam Zheng]

On Tue, 01/24 13:15, Paolo Bonzini wrote:
> 
> 
> On 24/01/2017 13:04, Fam Zheng wrote:
> > 
> > All in all I think we should skip external handlers regardless of
> > aio_disable_external(), or even skip try_poll_mode, in nested aio_poll()'s. 
> > The
> > reasons are 1) many nested aio_poll()'s don't have bdrv_drained_begin, so 
> > this
> > check is not sufficient [...] bdrv_flush()
> > spin longer than necessary, if not forever, when the guest keeps submitting 
> > more
> > requests with ioeventfd.
> 
> 
> I'm not sure I understand why this is related.  aio_poll() only tries
> poll mode once, so bdrv_flush would only spin until the fsync is complete.

Right, I was confused.  The problematic ones are "drain" style ones that tracks
a inflight counter. The only suspecious one is in v9fs_reset(), otherwise we are
safe!

Fam