Re: [PATCH] Set bit 1 in disabled processor's _STA

[Glauber Costa <glommer@redhat.com>]

On Mon, May 18, 2009 at 08:53:58AM +0300, Gleb Natapov wrote:
> On Mon, May 18, 2009 at 08:44:54AM +0300, Avi Kivity wrote:
> > Gleb Natapov wrote:
> >> On Sun, May 17, 2009 at 11:07:31PM +0300, Avi Kivity wrote:
> >>   
> >>> Gleb Natapov wrote:
> >>>     
> >>>> Theoretically we can provide different values for different OSes, but
> >>>> this is just a guess work since there is no any documentation how CPU
> >>>> hot-plug should work on x86.
> >>>>         
> >>> ACPI in fact supports this, but I hope we don't have to do that.
> >>>
> >>>     
> >> ACPI way is what I am talking about. Implement _OS object.
> >>   
> >
> > /*
> > * The story of _OSI(Linux)
> > *
> > * From pre-history through Linux-2.6.22,
> > * Linux responded TRUE upon a BIOS OSI(Linux) query.
> > *
> > * Unfortunately, reference BIOS writers got wind of this
> > * and put OSI(Linux) in their example code, quickly exposing
> > * this string as ill-conceived and opening the door to
> > * an un-bounded number of BIOS incompatibilities.
> > *
> > * For example, OSI(Linux) was used on resume to re-POST a
> > * video card on one system, because Linux at that time
> > * could not do a speedy restore in its native driver.
> > * But then upon gaining quick native restore capability,
> > * Linux has no way to tell the BIOS to skip the time-consuming
> > * POST -- putting Linux at a permanent performance disadvantage.
> > * On another system, the BIOS writer used OSI(Linux)
> > * to infer native OS support for IPMI!  On other systems,
> > * OSI(Linux) simply got in the way of Linux claiming to
> > * be compatible with other operating systems, exposing
> > * BIOS issues such as skipped device initialization.
> > *
> > * So "Linux" turned out to be a really poor chose of
> > * OSI string, and from Linux-2.6.23 onward we respond FALSE.
> > *
> > * BIOS writers should NOT query _OSI(Linux) on future systems.
> > * Linux will complain on the console when it sees it, and return FALSE.
> > * To get Linux to return TRUE for your system  will require
> > * a kernel source update to add a DMI entry,
> > * or boot with "acpi_osi=Linux"
> > */
> >
> > // Looks like no real content in this message?
> >
> Now I recall something on LKML about this. Well, in this case Linux
> shouldn't have used ACPI to invent its own way to do cpu hot-plug.
It didn't.
History shows that this method is what is used in some unisys machines,
which seems to be the only ones implementing this around.