Re: [Qemu-devel] [PATCH v2 11/11] block: Only poll block layer fds in bdrv_aio_poll

[Paolo Bonzini]

On 29/07/2015 13:53, Fam Zheng wrote:
>> > Yes, though I think you'd end up reverting patches 10 and 11 in the end.
> We will add outer disable/enable pairs to prevent another threads's aio_poll
> from sneaking in between bdrv_aio_poll calls, but we needn't obsolete
> bdrv_aio_poll() because of that - it can be useful by itself. For example
> bdrv_aio_cancel shouldn't look at ioeventfd, otherwise it could spin for too
> long on high load.  Does that make sense?

Did you mean bdrv_drain() (when it is not already surrounded by
disable/enable pairs in the caller)?  But yes, that makes sense.

I'm not sure that it makes sense to disable/enable in places such as
bdrv_pread.  The caller's block, if any, should suffice.  In this sense
you'd end up reverting large parts of patch 10.

Then you would have to see how many calls to bdrv_aio_poll are still
there, and how many can be converted with no semantic change to aio_poll
(e.g. there's no difference in qemu-img.c), and you'd end up reverting
patches 9 and 11 too.  But we can look at that later.

Paolo