Re: [patch 0/4] CPU Hotplug support for X86_64

Matthew Dobson
2005-05-25T22:17:31Z

Shaohua Li wrote:
> On Tue, 2005-05-24 at 01:11 -0700, Ashok Raj wrote:
>
>>TBD:
>>
>>1. Track down CONFIG_SCHED_SMT Oops with both cpu up/down.
>>2. Test on real NUMA hw.
>>
>
> With below patch, cpu hotplug works with SCHED_SMT enabled in my test.
> set_cpu_sibling_map is invoked before cpu is set to online.
>
> Thanks,
> Shaohua

I'm not sure, but you probably want "for_each_cpu(i)" instead of "for (i =
0; i < NR_CPUS; i++)" below.

It should be rare that you really want to explicitly itterate over
[0..NR_CPUS] cpus. for_each_cpu() will itterate over all "possible" cpus,
which may well be [0..NR_CPUS], but it at least is cleaner and more
readable. If your arch actually sets up cpu_possible_map correctly, then
it will likely be quite a bit faster and more efficient to use for_each_cpu().

Again, I haven't looked at the surrounding code, but it's very likely that
for_each_cpu() will do what you want.

-Matt

> --- a/arch/x86_64/kernel/smpboot.c.orig 2005-05-24 16:47:57.000000000 +0800
> +++ b/arch/x86_64/kernel/smpboot.c 2005-05-24 16:48:31.000000000 +0800
> @@ -443,7 +443,7 @@ set_cpu_sibling_map(int cpu)
> int i;
>
> if (smp_num_siblings > 1) {
> - for_each_online_cpu(i) {
> + for (i = 0; i < NR_CPUS; i++) {
> if (cpu_core_id[cpu] == cpu_core_id[i]) {
> cpu_set(i, cpu_sibling_map[cpu]);
> cpu_set(cpu, cpu_sibling_map[i]);
> @@ -454,7 +454,7 @@ set_cpu_sibling_map(int cpu)
> }
>
> if (current_cpu_data.x86_num_cores > 1) {
> - for_each_online_cpu(i) {
> + for (i = 0; i < NR_CPUS; i++) {
> if (phys_proc_id[cpu] == phys_proc_id[i]) {
> cpu_set(i, cpu_core_map[cpu]);
> cpu_set(cpu, cpu_core_map[i]);