[Xen-devel] RE: [PATCH] Align periodic vpts

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser
>Sent: Wednesday, February 11, 2009 7:34 PM
>
>On 11/02/2009 11:05, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
>
>> Aligned periodic vpts can improve the HVM guest power 
>consumption a lot,
>> especially while the guest using high HZ such as 1000HZ.
>> This patch aligns all periodic vpts except vlapic to the 
>period bound. For
>> vlapic, only make it aligned while using the new option 
>"align_periodic_vpt".
>> 
>> Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>
>
>Also, Intel already contributed code to merge up timers. It's the
>expiry-range patch in common/timer.c. This could be used by 
>vpt.c to add a
>per-domain acceptable range on vpt expiries. High-frequency 
>timers would
>then naturally fire together. Having a per-domain config 
>option for this
>would be something that would actually seem more generically 
>useful (could
>be used perhaps for other timers beyond vpt.c even).
>
>This seems to me a more intuitive and gracefully 
>selectable/de-selectable
>alternative to this proposed patch, which really looks like a hardcoded
>hack.
>

nice idea. But one quick think in my mind leads to one issue. Now
Xen timer doesn't differentiate single-shot or periodic timer. Then such
per-domain range option could also impact single-shot timer servicing
same domain... Of course current global slop option has same effect.
But it'd be better to mitigate the side effect on single-shot timer. Is it
feasible to add a new set_timer_range interface for explicit invocation,
e.g. by vpt, while still keeping original global slop option applying to all?

Thanks,
Kevin
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