From: Glauber de Oliveira Costa <glauber@xxxxxxxxxxxxxxx>
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@xxxxxxxxxx>