Greg, -----Original Message----- From: Greg KH [mailto:gregkh@linuxfoundation.org] Sent: 20141020 12:44 To: Neil Zhang Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] drivers: base: update cpu offline info when do hotplug On Mon, Oct 20, 2014 at 11:29:08AM +0800, Neil Zhang wrote: > The current per-cpu offline info won't be updated if it is hotplugged > in/out by a kernel governer. > Let's update it via cpu notifier. > > Signed-off-by: Neil Zhang > --- > drivers/base/cpu.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index > 006b1bc..9d61824 100644 > --- a/drivers/base/cpu.c > +++ b/drivers/base/cpu.c > @@ -418,10 +418,35 @@ static void __init > cpu_dev_register_generic(void) #endif } > > +static int device_hotplug_notifier(struct notifier_block *nfb, > + unsigned long action, void *hcpu) { > + unsigned int cpu = (unsigned long)hcpu; > + struct device *dev = get_cpu_device(cpu); > + int ret; > + > + switch (action & ~CPU_TASKS_FROZEN) { > + case CPU_ONLINE: > + dev->offline = false; > + ret = NOTIFY_OK; > + break; > + case CPU_DYING: > + dev->offline = true; > + ret = NOTIFY_OK; > + break; > + default: > + ret = NOTIFY_DONE; > + break; > + } > + > + return ret; > +} > + > void __init cpu_dev_init(void) > { > if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups)) > panic("Failed to register CPU subsystem"); > > cpu_dev_register_generic(); > + cpu_notifier(device_hotplug_notifier, 0); > } How much noise is this going to cause on a big/little system that constantly hot unplug/plugs processors all of the time? Can you explain more what kind of noise will be introduced on a big/little system? As I know IKS on arm will use cpu_suspend way to power down a core. But I don't know well about other architectures. Please give your suggestions. Thanks! greg k-h Best Regards, Neil Zhang {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I