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

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

>From: Keir Fraser
>Sent: Wednesday, February 11, 2009 7:23 PM
>
>On 11/02/2009 11:05, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
>
>> + * CAUTION:
>> + * While vlapic timer ticking too close to the pit.  We saw 
>a userspace
>> + * application getting the wrong answer because long CPU 
>bound sequences
>> + * appeared to run with zero CPU time. This only showed up 
>with old Linux
>> + * kernels (IIRC, it was with Red Hat 3 U8). So this option 
>may cause a
>> + * regression in this case.
>> + */
>> +static int opt_align_periodic_vpt = 0;
>> +boolean_param("align_periodic_vpt", opt_align_periodic_vpt);
>> +
>
>Presumably there are common cases where not aligning vlapic too has
>significant power overheads? Personally I'm not sure I care 

yes, it's necessary as average C-state residency is almost halved 
if not aligning, and thus draw higher power

Thanks
Kevin

>too much about a
>minor regression on RH3, if this patch is worthwhile at all I think it
>should be always on and at most have a domain config option. I 
>think a boot
>option will never ever be used.
>
> -- Keir
>
>
>
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