On Fri, 6 Oct 2006 16:10:12 -0700
Bryce Harrington <bryce at osdl.org> wrote:
> On Fri, Mar 17, 2006 at 01:04:12AM -0800, Andrew Morton wrote:
> > Srivatsa Vaddagiri <vatsa at in.ibm.com> wrote:
> > > Well ..other arch-es need to have a similar check if they get around to
> > > implement physical hot-add (even if they allow offlining of all CPUs). This is
> > > required since a user can (by mistake maybe) try to bring up an already online
> > > CPU by writing a '1' to it's sysfs 'online' file. 'store_online'
> > > (drivers/base/cpu.c) unconditionally calls 'smp_prepare_cpu' w/o checking for
> > > this error condition. The check added in the patch catches such error
> > > conditions as well.
> >
> > OK.. I guess we should fix those architectures while we're thinking about it.
> >
> > > + /* Check if CPU is already online. This can happen if user tries to
> > > + * bringup an already online CPU or a previous offline attempt
> > > + * on this CPU has failed.
> > > + */
> > > + if (cpu_online(cpu)) {
> > > + ret = -EINVAL;
> > > + goto exit;
> > > + }
> >
> > How well tested is this? From my reading, this will cause
> > enable_nonboot_cpus() to panic. Is that intended?
>
> Andrew,
>
> I wanted to give you an update on results of cpu testing I've done on
> recent kernels and several architectures. Since -rc1 is out, I wanted
> to give added visibility to the few issues that remain.
>
> The full results are available here:
>
> http://crucible.osdl.org/runs/hotplug_report.html
>
> This is actually a report for cpu hotplug tests generated hourly,
> however we run it against all of the kernel -git snapshots posted to
> kernel.org. Whereever you see a blank square, it indicates the kernel
> either failed to build or boot.
>
Can you describe the nature of the cpu-hotplug tests you're running? I'd
be fairly staggered if the kernel was able to survive a full-on cpu-hotplug
stress test for more than one second, frankly. There's a lot of code in
there which is non-hotplug-aware. Running a non-preemptible kernel would
make things appear more stable, perhaps.
iirc Pavel did some testing a month or two ago and was seeing userspace
misbehaviour?
>
> Issues were found in four areas: General kernel, cpu hotplug, sysstat,
> and the test harness itself.
>
It's surprising that AMD and Intel CPUs behave differently. Also a good
start on diagnosing things.
