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Date: Wed, 22 Dec 2010 16:27:27 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: shaohui.zheng@...el.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
haicheng.li@...ux.intel.com, lethal@...ux-sh.org,
ak@...ux.intel.com, shaohui.zheng@...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 Fri, 10 Dec 2010 15:31:24 +0800
shaohui.zheng@...el.com wrote:
> From: Shaohui Zheng <shaohui.zheng@...el.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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