lkml.org 
[lkml]   [2023]   [Mar]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v4] acpi/processor: fix evaluating _PDC method when running as Xen dom0
On Fri, Mar 17, 2023 at 1:42 PM Juergen Gross <jgross@suse.com> wrote:
>
> On 16.03.23 17:42, Roger Pau Monne wrote:
> > In ACPI systems, the OS can direct power management, as opposed to the
> > firmware. This OS-directed Power Management is called OSPM. Part of
> > telling the firmware that the OS going to direct power management is
> > making ACPI "_PDC" (Processor Driver Capabilities) calls. These _PDC
> > methods must be evaluated for every processor object. If these _PDC
> > calls are not completed for every processor it can lead to
> > inconsistency and later failures in things like the CPU frequency
> > driver.
> >
> > In a Xen system, the dom0 kernel is responsible for system-wide power
> > management. The dom0 kernel is in charge of OSPM. However, the
> > number of CPUs available to dom0 can be different than the number of
> > CPUs physically present on the system.
> >
> > This leads to a problem: the dom0 kernel needs to evaluate _PDC for
> > all the processors, but it can't always see them.
> >
> > In dom0 kernels, ignore the existing ACPI method for determining if a
> > processor is physically present because it might not be accurate.
> > Instead, ask the hypervisor for this information.
> >
> > Fix this by introducing a custom function to use when running as Xen
> > dom0 in order to check whether a processor object matches a CPU that's
> > online. Such checking is done using the existing information fetched
> > by the Xen pCPU subsystem, extending it to also store the ACPI ID.
> >
> > This ensures that _PDC method gets evaluated for all physically online
> > CPUs, regardless of the number of CPUs made available to dom0.
> >
> > Fixes: 5d554a7bb064 ('ACPI: processor: add internal processor_physically_present()')
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>
> Reviewed-by: Juergen Gross <jgross@suse.com>

Applied as 6.4 material under a slightly edited subject, thanks!

\
 
 \ /
  Last update: 2023-03-27 01:09    [W:0.049 / U:0.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site