Re: [PATCH 10/10] cpu bulk removal interface

[Shaohua Li <shaohua.li@intel.com>]

On Mon, 2006-05-08 at 01:31 -0500, Nathan Lynch wrote:
> Shaohua Li wrote:
> > 
> > Interface for bulk cpu removal. It's /sys/devices/system/cpu/cpu_bulk_remove
> > 
> > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> > ---
> > 
> >  linux-2.6.17-rc3-root/drivers/base/cpu.c  |   47 +++++++++++++++++++++++++++++-
> >  linux-2.6.17-rc3-root/include/linux/cpu.h |    3 +
> >  2 files changed, 49 insertions(+), 1 deletion(-)
> > 
> > diff -puN drivers/base/cpu.c~bulk_cpu_remove_interface drivers/base/cpu.c
> > --- linux-2.6.17-rc3/drivers/base/cpu.c~bulk_cpu_remove_interface	2006-05-07 07:47:02.000000000 +0800
> > +++ linux-2.6.17-rc3-root/drivers/base/cpu.c	2006-05-07 09:29:54.000000000 +0800
> > @@ -76,6 +76,46 @@ static inline void register_cpu_control(
> >  }
> >  #endif /* CONFIG_HOTPLUG_CPU */
> >  
> > +#ifdef CONFIG_BULK_CPU_REMOVE
> > +static ssize_t cpu_bulk_remove_show(struct sysdev_class *c, char *buf)
> > +{
> > +	int len;
> > +
> > +	len = cpulist_scnprintf(buf, PAGE_SIZE-1, cpu_online_map);
> > +	len += sprintf(buf + len, "\n");
> > +	return len;
> > +}
> 
> This doesn't really seem meaningful.  I'd say the attribute could do
> without a show method.
Ok, I'll remove it.

> > +static ssize_t cpu_bulk_remove_store(struct sysdev_class *c,
> > +	const char *buf, size_t count)
> > +{
> > +	int err;
> > +	cpumask_t removed_cpus;
> > +
> > +	if ((err = lock_cpu_hotplug_interruptible() != 0))
> > +		return err;
> > +	err = cpulist_parse(buf, removed_cpus);
> > +	if (err) {
> > +		unlock_cpu_hotplug();
> > +		return err;
> > +	}
> > +
> > +	unlock_cpu_hotplug();
> > +	cpu_down_mask(removed_cpus);
> > +	return count;
> > +}
> 
> Shouldn't this make sure that we don't offline all cpus?
cpu_down_mask will check it.

> Why are you using lock_cpu_hotplug_interruptible instead of
> lock_cpu_hotplug?
> 
> Why is only the parsing of the cpumask buffer protected by the cpu
> hotplug lock?  Shouldn't cpu_down_mask be called with the lock held?
we actually don't need lock here. I'll remove it.

> Can cpu_down_mask fail, and if so, shouldn't we be reporting the
> error?
Makes sense.

Thanks,
Shaohua