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

["Wei, Gang" <gang.wei@xxxxxxxxx>]

On Wednesday, February 11, 2009 9:21 PM, Tian, Kevin wrote:
>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: Wednesday, February 11, 2009 9:06 PM
>> 
>> I'd actually be interested in knowing how just bumping Xen
>> cmdline option
>> timer_slop= would influence power usage and guest timers. No new code
>> needed, a nice sliding dial (per host) for power usage versus timer accuracy.
...
> So range timer does affects latency, but in general is a power
> efficient feature to fit requirement where power matters more. It's
> especially useful at cpu over-commitment where more chances
> to align timers and reduce interrupts by a higher factor.
> 
> While range timer impacts all timers nondistinctively (xen timer
> itself is in essential one shot), Jimmy's patch tends to reach
> similar effect for periodical timer (since once align at 1st shot,
> so does latter), while leaving single shot timer as it is w/o touching
> global slop.
> 
> To me above two are not identical which reduces power in different
> level.:-)

Just as Kevin explained, aligning periodic timer in the beginning could bring 
powe gain with less impact to timer expiry accuracy, so it is suitable for 
using before we dig out most of the side effect for large slop range timer. I 
will try to make the option per-domain and then resend the patch. Meanwhile, I 
am also prefer to make this option default on. Any further comments?

Jimmy
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