Re: [Qemu-devel] [PATCH] [RFC] aio/async: Add timed bottom-halves

[Alex Bligh]

Stefan,

--On 17 July 2013 11:02:30 +0800 Stefan Hajnoczi <address@hidden> wrote:

> The steps to achieving this:
>
> 1. Drop alarm timers from qemu-timer.c and calculate g_poll() timeout
>    instead for the main loop.
>
> 2. Introduce a per-AioContext aio_ctx_clock that can be used with
>    qemu_new_timer() to create a QEMUTimer that expires during
>    aio_poll().
>
> 3. Calculate g_poll() timeout for aio_ctx_clock in aio_poll().

I've pretty much written this.

Two issues:

1. I very much enjoyed deleting all the alarm timers code. However, it was
  doing something vaguely useful, which was calling qemu_notify_event
  when the timer expired. Under the new regime above, if the AioContext
  clock's timers expires within aio_poll, life is good as the timeout
  to g_poll will expire. However, this won't apply if any of the other
  three static clock's timers expire. Also, it won't work within the
  mainloop poll. Also, we lose the ability to respond to timers in a sub
  millisecond way.

  Options:

  a) restore alarm timers (at least for the time being). Make all
     alarm timers do qemu_notify_event. However, only run the AioContext
     clock's timers within aio_poll. This is the least intrusive change.

  b) calculate the timeout in aio_poll with respect to the minimum
     deadline across all clocks, not just AioContext's clock. Use the
     same logic in mainloop.

  I'd go for (b), except for the millisecond accuracy thing. So my
  temptation (sadly) is (a).

2. If we do delete alarm timers, I'll need to delete the -clock option.

WDYT?

--
Alex Bligh