Re: [Xen-devel] [PATCH v3 2/3] xen, cpu_hotplug: call device_offline instead of cpu_down

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/20/2015 06:28 AM, Stefano Stabellini wrote:
> On Mon, 19 Oct 2015, Boris Ostrovsky wrote:
> > On 10/19/2015 12:55 PM, Stefano Stabellini wrote:
> > > When offlining a cpu, instead of cpu_down, call device_offline, which
> > > also takes care of updating the cpu.dev.offline field. This keeps the
> > > sysfs file /sys/devices/system/cpu/cpuN/online, up to date.  Also move
> > > the call to disable_hotplug_cpu, because it makes more sense to have it
> > > there.
> > >
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > CC: konrad.wilk@xxxxxxxxxx
> > > CC: boris.ostrovsky@xxxxxxxxxx
> > > CC: david.vrabel@xxxxxxxxxx
> > > ---
> > >    drivers/xen/cpu_hotplug.c |    3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
> > > index 43de1f5..78804b5 100644
> > > --- a/drivers/xen/cpu_hotplug.c
> > > +++ b/drivers/xen/cpu_hotplug.c
> > > @@ -18,6 +18,8 @@ static void enable_hotplug_cpu(int cpu)
> > >      static void disable_hotplug_cpu(int cpu)
> > >    {
> > > +       if (cpu_online(cpu))
> > > +               device_offline(get_cpu_device(cpu));
> > >         if (cpu_present(cpu))
> > >                 xen_arch_unregister_cpu(cpu);
> > Do we want to call device_online() when plugging cpu in?
> I don't know: that would automatically bring the cpu online after the
> user hot-plugs it. Is it what we want? Current one would have to manually:
>
> echo 1 > /sys/devices/system/cpu/cpu1/online
>
> I thought that was the expected behaviour?
Right, we should keep onlining as an explicit operation. I think it's 
worth mentioning in the commit message why we don't call device_online() 
while using device_offline(), which is its complement.

-boris


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