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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

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 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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