Re: Fix migration issue when the destination is loaded

[Mark McLoughlin <markmc@redhat.com>]

Hi Dor,

On Wed, 2009-07-15 at 18:03 +0300, Dor Laor wrote:
> If the migration socket is full, we get EAGAIN for the write.
> The set_fd_handler2 defers the write for later on. The function
> tries to wake up the iothread by qemu_kvm_notify_work.
> Since this happens in a loop, multiple times, the pipe that emulates
> eventfd becomes full and we get a deadlock.

I'm not sure I follow:

  - You're seeing qemu_kvm_notify_work() being called many times

  - The call chain is migrate_fd_put_buffer(), qemu_set_fd_handler2(), 
    main_loop_break()

  - This happens when write() in migrate_fd_put_buffer() returns EAGAIN 
    because the socket buffer has filled up

Correct?

That sounds like migrate_fd_put_buffer() is being called repeatedly
while we know the socket isn't writable?

Shouldn't the buffered file could stop attempting to call put_buffer()
until it has been notified that the underlying fd is writable?

Cheers,
Mark.