Re: early_cpu_init() and identify_cpu()

[Keir Fraser <keir@xensource.com>]

On 13/7/07 17:16, "Jan Beulich" <jbeulich@novell.com> wrote:

> Is there any reason (other than having things inherited this way from Linux)
> that
> we cannot call identify_cpu() for the boot CPU at the end of early_cpu_init()
> rather than explicitly from __start_xen()? And if not, it would seem
> reasonable
> to me to at once move the two CR4 twiddling pieces out of __start_xen, too.
> 
> (I'm not asking because I want to beautify the code, but because I want the
> identify to happen earlier, namely I want to fully set up the VESA console as
> early as possible, but there I'd like to be able to set MTRRs, which in turn
> depends on identify_cpu() having executed.

Isn't it a fairly safe bet that the BIOS will have done this for us and, if
not, that the penalty is a performance loss (probably using WB or UC instead
of WC) rather than a correctness issue? And hence, if we bother to update
the MTRRs at all, then it can at least be left until later in the boot?

 -- Keir