Re: [Qemu-devel] [PATCH v2] block: avoid SIGUSR2

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/19/2011 05:11 PM, Kevin Wolf wrote:
>> >  I think it is possible to go a step further, turn
>> >  posix_aio_process_queue into a bottom half and get rid of the pipe
>> >  altogether.  This in turn would remove the only real user of
>> >  io_process_queue in qemu_aio_set_fd_handler.  However, this is already a
>> >  nice improvement.
> But without the fd, wouldn't the I/O thread possibly wait for much
> longer until its select() times out and it starts processing BHs?

Hmm, in qemu_aio_wait yes...  In the normal qemu event loop, however, 
bottom halves exit the select loop with qemu_notify_event().  qemu 
currently has a 1-second timeout for the select, but it should work just 
as well with an infinite timeout.  If it doesn't, it's a bug.

It should be possible to turn posix_aio_process_queue into a bottom 
half, but the pipe is still necessary in order to exit the qemu_aio_wait 
select loop and schedule the bottom half.

Paolo