Re: [PATCH] raise tsc clocksource rating

Rusty Russell
2007-10-30T02:39:23Z

On Tuesday 30 October 2007 09:17:38 Thomas Gleixner wrote:
> On Mon, 29 Oct 2007, Glauber de Oliveira Costa wrote:
>
> CC'ed John and removed glauber@t60.localdomain :)
>
> > From: Glauber de Oliveira Costa <glauber@t60.localdomain>
> >
> > tsc is very good time source (when it does not have drifts, does not
> > change it's frequency, i.e. when it works), so it should have its rating
> > raised to a value greater than, or equal 400.
> >
> > Since it's being a tendency among paravirt clocksources to use values
> > around 400, we should declare tsc as even better: So we use 500.
> >
> > This patch also touches the comments on clocksource.h, which suggests
> > that 499 would be a limit on the rating values.
> >
> > Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
>
> Acked-by: Thomas Gleixner <tglx@linutronix.de>

No. tsc is very good, it's not perfect. If a paravirt clock registers 400 it
really means "pick me over the tsc".

That's *why* they use > 400: it's in the documentation.

Rusty.