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

[Fam Zheng <famz@redhat.com>]

On Wed, 07/29 14:03, Paolo Bonzini wrote:
> 
> 
> 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.
> 

Okay.

There 19 bdrv_aio_poll()'s after this series:

block.c                bdrv_create
block/curl.c           curl_init_state
block/io.c             bdrv_drain
block/io.c             bdrv_drain_all
block/io.c             bdrv_prwv_co
block/io.c             bdrv_get_block_status_above
block/io.c             bdrv_aio_cancel
block/io.c             bdrv_flush
block/io.c             bdrv_discard
block/io.c             bdrv_flush_io_queue
block/nfs.c            nfs_get_allocated_file_size
block/qed-table.c      qed_read_l1_table_sync
block/qed-table.c      qed_write_l1_table_sync
block/qed-table.c      qed_read_l2_table_sync
block/qed-table.c      qed_write_l2_table_sync
blockjob.c             block_job_finish_sync
include/block/block.h  bdrv_get_stats
qemu-img.c             run_block_job
qemu-io-cmds.c         do_co_write_zeroes
qemu-io-cmds.c         wait_break_f

Most of them make some sense to me, but not many make a real difference.  The
most important ones should be bdrv_drain* and bdrv_flush, and can be taken care
of from caller side.

Fam