Messages in this thread | | | Date | Wed, 22 Dec 2010 16:27:27 -0800 | From | Andrew Morton <> | Subject | Re: [5/7, v9] NUMA Hotplug Emulator: Support cpu probe/release in x86_64 |
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On Fri, 10 Dec 2010 15:31:24 +0800 shaohui.zheng@intel.com wrote:
> From: Shaohui Zheng <shaohui.zheng@intel.com> > > CPU physical hot-add/hot-remove are supported on some hardwares, and it > was already supported in current linux kernel. NUMA Hotplug Emulator provides > a mechanism to emulate the process with software method. It can be used for > testing or debuging purpose. > > CPU physical hotplug is different with logical CPU online/offline. Logical > online/offline is controled by interface /sys/device/cpu/cpuX/online. CPU > hotplug emulator uses probe/release interface. It becomes possible to do cpu > hotplug automation and stress > > Add cpu interface probe/release under sysfs for x86_64. User can use this > interface to emulate the cpu hot-add and hot-remove process. > > Directive: > *) Reserve CPU thru grub parameter like: > maxcpus=4 > > the rest CPUs will not be initiliazed. > > *) Probe CPU > we can use the probe interface to hot-add new CPUs: > echo nid > /sys/devices/system/cpu/probe > > *) Release a CPU > echo cpu > /sys/devices/system/cpu/release > > A reserved CPU will be hot-added to the specified node. > 1) nid == 0, the CPU will be added to the real node which the CPU > should be in > 2) nid != 0, add the CPU to node nid even through it is a fake node. > > > ... > > --- linux-hpe4.orig/arch/x86/kernel/topology.c 2010-12-10 14:39:43.333331000 +0800 > +++ linux-hpe4/arch/x86/kernel/topology.c 2010-12-10 14:49:56.043331000 +0800 > @@ -30,6 +30,9 @@ > #include <linux/init.h> > #include <linux/smp.h> > #include <asm/cpu.h> > +#include <linux/cpu.h> > +#include <linux/topology.h> > +#include <linux/acpi.h> > > static DEFINE_PER_CPU(struct x86_cpu, cpu_devices); > > @@ -66,6 +69,78 @@ > unregister_cpu(&per_cpu(cpu_devices, num).cpu); > } > EXPORT_SYMBOL(arch_unregister_cpu); > + > +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.
> + /* check parameters */ > + if (!buf || count < 2) > + return -EPERM; > + > + nid = simple_strtoul(buf, NULL, 0);
checkpatch?
> + printk(KERN_DEBUG "Add a cpu to node : %d\n", nid);
"Add a CPU to node %d" would make more sense.
> + 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"
> + 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.
> + if (per_cpu(cpu_sys_devices, num) == NULL) { > + selected = num;
Similarly, I'd have used "selected_cpu".
> + 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.
> +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.
> + /* 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.
> + 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".
> + return -EPERM; > + } > + > + } > + > + arch_unregister_cpu(cpu); > + acpi_unmap_lsapic(cpu); > + > + return count; > +} > +EXPORT_SYMBOL(arch_cpu_release);
No 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.".
> + 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.
> static ssize_t show_online(struct sys_device *dev, struct sysdev_attribute *attr, > char *buf) > { > > ... >
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