Re: [Qemu-devel] timer issue on 1.7.0 and later

[Alex Bligh]

On 13 Feb 2014, at 15:36, Peter Maydell wrote:

> On 10 February 2014 17:15, Rob Herring <address@hidden> wrote:
>> This doesn't appear to be too useful. The AvgLength is large because
>> INT64_MAX / GTIMER_SCALE is used as the next timer value when no timer
>> is needed.
> 
> The code already uses timer_del() when no next timer is needed
> (that's the "timer disabled" case in gt_recalc_timer()). We only
> set the timer to INT64_MAX / GTIMER_SCALE for the case where the
> architecture demands an interrupt occurs in the really distant
> future. Admittedly the chances of QEMU still running in 200 years
> time are quite low, but it seemed at the time to be better to just
> write the code to behave correctly, since I assumed that calling
> timer_mod with a large timeout wasn't going to be really more
> expensive than calling timer_del. (Looking at the code, we end
> up walking the list of timers twice rather than once.)

I suspect the issue is not walking the lists, but calling
qemu_notify, breaking out of mainloop select etc. etc.; that
happens on a timer_modify but not on a timer_del. We could
fix this so that it only happened if the timer's expiry
time was reduced in timer_mod (I think).

-- 
Alex Bligh