lkml.org 
[lkml]   [2012]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRE: [PATCH v5 03/12] x86/topology.c: Support functions for CPU0 online/offline
From
Date
On Tue, 2012-01-24 at 22:31 +0000, Yu, Fenghua wrote:
> > On Wed, 2012-01-11 at 09:04 -0800, Fenghua Yu wrote:
> > > From: Fenghua Yu <fenghua.yu@intel.com>
> > >
> > > If CONFIG_BOOTPARAM_HOTPLUG_CPU is turned on, CPU0 hotplug feature is
> > enabled
> > > by default.
> > >
> > > If CONFIG_BOOTPARAM_HOTPLUG_CPU is not turned on, CPU0 hotplug
> > feature is not
> > > enabled by default. The kernel parameter cpu0_hotplug can enable CPU0
> > hotplug
> > > feature at boot.
> > [...]
> > > int __ref arch_register_cpu(int num)
> > > {
> > > /*
> > > - * CPU0 cannot be offlined due to several
> > > - * restrictions and assumptions in kernel. This basically
> > > - * doesn't add a control file, one cannot attempt to offline
> > > - * BSP.
> > > + * Two known BSP/CPU0 dependencies: Resume from suspend/hibernate
> > > + * depends on BSP. PIC interrupts depend on BSP.
> > > *
> > > - * Also certain PCI quirks require not to enable hotplug control
> > > - * for all CPU's.
> > > + * If the BSP depencies are under control, one can tell kernel to
> > > + * enable BSP hotplug. This basically adds a control file and
> > > + * one can attempt to offline BSP.
> > > */
> > > - if (num)
> > > + if (num || cpu0_hotpluggable)
> > > per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
> > >
> > > return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
> >
> > This change belongs at the end of the series. It should not be
> > possible
> > to enable CPU0 hotplug until after the hotplug logic can do it
> > correctly, and this might break bisection.
>
> Quote from https://www.linux.com/how-to-participate-in-the-linux-community
> "It can be tempting to add a whole new infrastructure with a series of
> patches, but to leave that infrastructure unused until the final patch
> in the series enables the whole thing. This temptation should be
> avoided if possible; if that series adds regressions, bisection will
> finger the last patch as the one which caused the problem, even though
> the real bug is elsewhere. Whenever possible, a patch which adds new
> code should make that code active immediately."
>
> So this patch currently is in the right place in the patch set unless
> I miss something.

You're giving undue weight to that guidance. It is far more important
that you do not enable features that don't work!

Ben.

--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.



\
 
 \ /
  Last update: 2012-01-24 23:55    [W:0.056 / U:0.160 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site