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

[Alex Bligh]

--On 6 July 2013 17:24:57 +0100 Alex Bligh <address@hidden> wrote:

> Add timed bottom halves. A timed bottom half is a bottom half that
> will not execute until a given time has passed (qemu_bh_schedule_at)
> or a given interval has passed (qemu_bh_schedule_in). Any qemu
> clock can be used, and times are specified in nanoseconds.

For background, this patch resulted from a discussion with Kevin & Stefan
on IRC as to the best way to use timers (or rather avoid using timers)
in block drivers.

There is one thing I'm not entirely sure about:

> +void qemu_bh_schedule_at(QEMUBH *bh, QEMUClock *clock, int64_t time)
> +{
> +    /* Allow rescheduling if already scheduled */
> +    bh->scheduled = 1;
> +    bh->idle = 0;
> +    bh->clock = clock;
> +    bh->time = time;
> +    aio_notify(bh->ctx); /*FIXME: is this right?*/
> +}

qemu_bh_schedule calls aio_notify, but qemu_bh_schedule_idle does
not. I am not quite sure why the latter doesn't - possibly through
not fully understanding the aio system. Should qemu_bh_schedule_at
be calling this, when I don't know whether the bh is scheduled
for 1 nanosecond ahead or 1 second?

--
Alex Bligh