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

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

>From: Tian, Kevin
>Sent: Wednesday, February 11, 2009 7:48 PM
>
>>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?
>

Think it more, I think that Jimmy's patch is simpler and more 
accurate for the purpose. It's just a one-time adjustment for
periodical timer, and no harm to single-shot timer. It can be
enabled by default, while per-domain range has side-effect 
unless adding more code to differentiate timers which is not
worthy. 

Of course per-domain switch is still required to disable it as
your previous comment, for old guest.

Thanks,
Kevin
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