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Date: Thu, 25 Jul 2013 11:19:29 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [PATCHv2] [RFC 2/7] aio / timers: qemu-timer.c
 utility functions and add list of clocks
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To: Alex Bligh <alex@alex.org.uk>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, rth@twiddle.net

On Sat, Jul 20, 2013 at 07:06:38PM +0100, Alex Bligh wrote:
> Add utility functions to qemu-timer.c for nanosecond timing.
> 
> Ensure we keep track of all QEMUClocks on a list.
> 
> Add qemu_clock_deadline_ns and qemu_clock_deadline_all_ns to
> calculate deadlines to nanosecond accuracy.
> 
> Add utility function qemu_soonest_timeout to calculate soonest deadline.
> 
> Add qemu_timeout_ns_to_ms to convert a timeout in nanoseconds back to
> milliseconds for when ppoll is not used.

Please split this into smaller patches.  There are several logical
changes happening here.

> @@ -61,6 +71,15 @@ int64_t cpu_get_ticks(void);
>  void cpu_enable_ticks(void);
>  void cpu_disable_ticks(void);
>  
> +static inline int64_t qemu_soonest_timeout(int64_t timeout1, int64_t timeout2)
> +{
> +    /* we can abuse the fact that -1 (which means infinite) is a maximal
> +     * value when cast to unsigned. As this is disgusting, it's kept in
> +     * one inline function.
> +     */
> +    return ((uint64_t) timeout1 < (uint64_t) timeout2) ? timeout1 : timeout2;

The straightforward version isn't much longer than the commented casting trick:

if (timeout1 == -1) {
    return timeout2;
} else if (timeout2 == -1) {
    return timeout1;
} else {
    return timeout1 < timeout2 ? timeout1 : timeout2;
}

> @@ -48,6 +44,8 @@ struct QEMUClock {
>  
>      int type;
>      bool enabled;
> +
> +    QLIST_ENTRY(QEMUClock) list;

I don't think global state is necessary.  The
run_timers()/clock_deadline() users have QEMUClock references, they can
just call per-QEMUClock functions instead of requiring qemu-timers.c to
keep a list.

This way AioContext clocks are safe to use from threads.

> +void qemu_free_clock(QEMUClock *clock)
> +{
> +    QLIST_REMOVE(clock, list);
> +    g_free(clock);

assert that there are no timers left?