Re: [Qemu-devel] [PATCH] spapr: Correctly set query_hotpluggable_cpus hook based on machine version

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 5 Aug 2016 20:21:59 +0530
Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:

> On Fri, Aug 05, 2016 at 05:50:29PM +1000, David Gibson wrote:
> > Prior to c8721d3 "spapr: Error out when CPU hotplug is attempted on older
> > pseries machines", attempting to use query-hotpluggable-cpus on pseries-2.6
> > and earlier machine types would SEGV.
> > 
> > That change fixed that, but due to some unexpected interactions in init
> > order and a brown-paper-bag worthy failure to test, it accidentally
> > disabled query-hotpluggable-cpus for all pseries machine types, including
> > the current one which should allow it.
> > 
> > In fact, query_hotpluggable_cpus needs to be non-NULL when and only when
> > the dr_cpu_enabled flag in sPAPRMachineClass is set, which makes
> > dr_cpu_enabled itself redundant.
> > 
> > This patch removes dr_cpu_enabled, instead directly setting
> > query_hotpluggable_cpus from the machine class_init functions, and using
> > that to determine the availability of CPU hotplug when necessary.  
> 
> dr_cpu_enabled actually determines if CPU hotplug feature is present
> or not. It also controls the creation of DRC-specific properties
> in /cpus DT node like ibm,drc-indexes etc
> 
> query_hotpluggable_cpus just tells us if the machine supports the
> querying of hotpluggable CPUS. query_hotpluggable_cpus definitely
> implies dr_cpu_enabled but dr_cpu_enabled can exist on its own
> (theoretically at the least) without query_hotpluggable_cpus.
> 
> So I think we should not replace dr_cpu_enabled with query_hotpluggable_cpus.
I agree, hotplug capability shouldn't depend on availability of
interface to operate it but rather on some platform specific bits
which dr_cpu_enabled is (or at least looks like it's).


> 
> However, I tested this patch and it works as intended.
> 
> Regards,
> Bharata.
> 
>