Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads

Srivatsa S. Bhat
2012-06-14T08:33:00Z

On 06/13/2012 04:30 PM, Thomas Gleixner wrote:

> Provide a generic interface for setting up and tearing down percpu
> threads.
>
> On registration the threads for already online cpus are created and
> started. On deregistration (modules) the threads are stoppped.
>
> During hotplug operations the threads are created, started, parked and
> unparked. The datastructure for registration provides a pointer to
> percpu storage space and optional setup, cleanup, park, unpark
> functions. These functions are called when the thread state changes.
>
> Thread functions should look like the following:
>
> int thread_fn(void *cookie)
> {
> while (!smpboot_thread_check_parking(cookie)) {
> do_stuff();
> }
> return 0;
> }
>

This patchset looks great! But I have some comments below:

> Index: tip/kernel/cpu.c
> ===================================================================
> --- tip.orig/kernel/cpu.c
> +++ tip/kernel/cpu.c
> @@ -280,6 +280,7 @@ static int __ref _cpu_down(unsigned int
> __func__, cpu);
> goto out_release;
> }
> + smpboot_park_threads(cpu);
>

If cpu_down fails further down, don't we want to unpark these threads
as part of error recovery?

> err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> if (err) {
> @@ -354,6 +355,10 @@ static int __cpuinit _cpu_up(unsigned in
> goto out;
> }
>
> + ret = smpboot_create_threads(cpu);
> + if (ret)
> + goto out;
> +

Here also, we might want to clean up on error right?

> ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
> if (ret) {
> nr_calls--;
> @@ -370,6 +375,7 @@ static int __cpuinit _cpu_up(unsigned in
>
> /* Now call notifier in preparation. */
> cpu_notify(CPU_ONLINE | mod, hcpu);
> + smpboot_unpark_threads(cpu);
>
> out_notify:
> if (ret != 0)

Regards,
Srivatsa S. Bhat