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Date: Thu, 23 Dec 2010 09:34:10 +0800
From: Shaohui Zheng <shaohui.zheng@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: shaohui.zheng@...el.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
lethal@...ux-sh.org, ak@...ux.intel.com, rientjes@...gle.com,
dave@...ux.vnet.ibm.com, gregkh@...e.de,
Ingo Molnar <mingo@...e.hu>, Len Brown <len.brown@...el.com>,
Yinghai Lu <Yinghai.Lu@....COM>, Tejun Heo <tj@...nel.org>,
Haicheng Li <haicheng.li@...el.com>
Subject: Re: [5/7, v9] NUMA Hotplug Emulator: Support cpu probe/release in
x86_64
On Wed, Dec 22, 2010 at 04:27:27PM -0800, Andrew Morton wrote:
> On Fri, 10 Dec 2010 15:31:24 +0800
> > +
> > +ssize_t arch_cpu_probe(const char *buf, size_t count)
> > +{
> > + int nid = 0;
> > + int num = 0, selected = 0;
>
> One definition per line make for more maintainable code.
>
> Two of these initialisations are unnecessary.
>
Agree, I will put them into 2 lines, and remove the initialisations.
I always try to initialize them when we define it, it seems that it is a bad habit.
> > + /* check parameters */
> > + if (!buf || count < 2)
> > + return -EPERM;
> > +
> > + nid = simple_strtoul(buf, NULL, 0);
>
> checkpatch?
it is a warning, so I ignore it.
I will solve it.
>
> > + printk(KERN_DEBUG "Add a cpu to node : %d\n", nid);
>
> "Add a CPU to node %d" would make more sense.
>
Get it.
> > + if (nid < 0 || nid > nr_node_ids - 1) {
> > + printk(KERN_ERR "Invalid NUMA node id: %d (0 <= nid < %d).\n",
> > + nid, nr_node_ids);
> > + return -EPERM;
> > + }
> > +
> > + if (!node_online(nid)) {
> > + printk(KERN_ERR "NUMA node %d is not online, give up.\n", nid);
>
> "giving"
>
Get it.
> > + return -EPERM;
> > + }
> > +
> > + /* find first uninitialized cpu */
> > + for_each_present_cpu(num) {
>
> s/num/cpu/ would be conventional. "num" is a pretty poor identifier in
> general - it fails to identify what it is counting.
>
I will replace the identifier 'num' with 'cpu'.
> > + if (per_cpu(cpu_sys_devices, num) == NULL) {
> > + selected = num;
>
> Similarly, I'd have used "selected_cpu".
>
Get it.
> > + break;
> > + }
> > + }
> > +
> > + if (selected >= num_possible_cpus()) {
> > + printk(KERN_ERR "No free cpu, give up cpu probing.\n");
> > + return -EPERM;
> > + }
> > +
> > + /* register cpu */
> > + arch_register_cpu_node(selected, nid);
> > + acpi_map_lsapic_emu(selected, nid);
> > +
> > + return count;
> > +}
> > +EXPORT_SYMBOL(arch_cpu_probe);
>
> arch_cpu_probe() is global and exported to modules, but is undocumented.
>
> If it had been documented, I might have been able to work out why arg
> `count' is checked, but never used.
>
Sorry, Andrew, I did not catch it. Do you mean to add the document before
the definition of the function arch_cpu_probe?
> > +ssize_t arch_cpu_release(const char *buf, size_t count)
> > +{
> > + int cpu = 0;
> > +
> > + cpu = simple_strtoul(buf, NULL, 0);
>
> unneeded initialisation, spurious whitespace, checkpatch.
>
Agree.
> > + /* cpu 0 is not hotplugable */
> > + if (cpu == 0) {
> > + printk(KERN_ERR "can not release cpu 0.\n");
>
> It's generally better to make kernel messages self-identifying.
> Especially error messages. If someone comes along and sees "can not
> release cpu 0" in their logs, they don't have a clue what caused it
> unless they download the kernel sources and go grepping.
>
How about "arch_cpu_release: can not release cpu 0.\n"?
> > + return -EPERM;
> > + }
> > +
> > + if (cpu_online(cpu)) {
> > + printk(KERN_DEBUG "offline cpu %d.\n", cpu);
> > + if (!cpu_down(cpu)) {
> > + printk(KERN_ERR "fail to offline cpu %d, give up.\n", cpu);
>
> "failed", "giving".
>
Get it.
> > + return -EPERM;
> > + }
> > +
> > + }
> > +
> > + arch_unregister_cpu(cpu);
> > + acpi_unmap_lsapic(cpu);
> > +
> > + return count;
> > +}
> > +EXPORT_SYMBOL(arch_cpu_release);
>
> No documentation.
>
Sorry, It is the same with function arch_cpu_probe, I did not catch the
problem, should I add documentation before the definition or declaration? Or
add the documentation into directory Documentation/.
> > #else /* CONFIG_HOTPLUG_CPU */
> >
> > static int __init arch_register_cpu(int num)
> > @@ -83,8 +158,14 @@
> > register_one_node(i);
> > #endif
> >
> > - for_each_present_cpu(i)
> > - arch_register_cpu(i);
> > + /*
> > + * when cpu hotplug emulation enabled, register the online cpu only,
> > + * the rests are reserved for cpu probe.
> > + */
>
> Something like "When cpu hotplug emulation is enabled, register only
> the online cpu. The remainder are reserved for cpu probing.".
>
>
Get it.
> > + for_each_present_cpu(i) {
> > + if ((cpu_hpe_on && cpu_online(i)) || !cpu_hpe_on)
> > + arch_register_cpu(i);
> > + }
> >
> > return 0;
> > }
> >
> > ...
> >
> > --- linux-hpe4.orig/drivers/acpi/processor_driver.c 2010-12-10 13:42:34.593331000 +0800
> > +++ linux-hpe4/drivers/acpi/processor_driver.c 2010-12-10 14:48:32.143331001 +0800
> > @@ -542,6 +542,14 @@
> > goto err_free_cpumask;
> >
> > sysdev = get_cpu_sysdev(pr->id);
> > + /*
> > + * Reserve cpu for hotplug emulation, the reserved cpu can be hot-added
> > + * throu the cpu probe interface. Return directly.
>
> s/emulation, the/emulation. The/
> s/throu/through/
>
> > + */
> > + if (sysdev == NULL) {
> > + goto out;
> > + }
>
> Unneeded braces.
>
> > if (sysfs_create_link(&device->dev.kobj, &sysdev->kobj, "sysdev")) {
> > result = -EFAULT;
> > goto err_remove_fs;
> > @@ -582,6 +590,7 @@
> > goto err_remove_sysfs;
> > }
> >
> > +out:
> > return 0;
> >
> >
> > ...
> >
> > --- linux-hpe4.orig/drivers/base/cpu.c 2010-12-10 14:39:43.333331000 +0800
> > +++ linux-hpe4/drivers/base/cpu.c 2010-12-10 14:48:32.143331001 +0800
> > @@ -22,9 +22,15 @@
> > };
> > EXPORT_SYMBOL(cpu_sysdev_class);
> >
> > -static DEFINE_PER_CPU(struct sys_device *, cpu_sys_devices);
> > +DEFINE_PER_CPU(struct sys_device *, cpu_sys_devices);
> >
> > #ifdef CONFIG_HOTPLUG_CPU
> > +/*
> > + * cpu_hpe_on is a switch to enable/disable cpu hotplug emulation. it is
>
> s/it/It/.
>
> > + * disabled in default, we can enable it throu grub parameter cpu_hpe=on
>
> "through".
>
> > + */
> > +int cpu_hpe_on;
>
> __read_mostly, perhaps.
>
CPU Hotplug emulation is for debug purpose, so cpu_hpe_on is not used very frequently.
> > static ssize_t show_online(struct sys_device *dev, struct sysdev_attribute *attr,
> > char *buf)
> > {
> >
> > ...
> >
--
Thanks & Regards,
Shaohui
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