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SubjectRe: [PATCH] cpu/hotplug: Provide dynamic range for prepare stage
----- On Jan 10, 2017, at 8:01 AM, Thomas Gleixner tglx@linutronix.de wrote:

> Mathieu reported that the LTTNG modules are broken as of 4.10-rc1 due to
> the removal of the cpu hotplug notifiers.
>
> Usually I don't care much about out of tree modules, but LTTNG is widely
> used in distros. There are two ways to solve that:
>
> 1) Reserve a hotplug state for LTTNG
>
> 2) Add a dynamic range for the prepare states.
>
> While #1 is the simplest solution, #2 is the proper one as we can convert
> in tree users, which do not care about ordering, to the dynamic range as
> well.
>
> Add a dynamic range which allows LTTNG to request states in the prepare
> stage.

I prepared a lttng-modules commit [1] that uses CPUHP_BP_PREPARE_DYN on 4.10
kernels, and it works fine through my cpu hotplug stress-testing. It's a very
good cleanup! Thanks Thomas for this nice API.

I'll be able to merge my commit into lttng-modules as soon as your patch
lands into Linux mainline.

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Tested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thanks,

Mathieu

[1] https://github.com/compudj/lttng-modules-dev/commit/f02214ac2e9a0f3d8d0270c0ac702c3143cdf120

>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> ---
>
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 20bfefbe7594..d936a0021839 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -74,6 +74,8 @@ enum cpuhp_state {
> CPUHP_ZCOMP_PREPARE,
> CPUHP_TIMERS_DEAD,
> CPUHP_MIPS_SOC_PREPARE,
> + CPUHP_BP_PREPARE_DYN,
> + CPUHP_BP_PREPARE_DYN_END = CPUHP_BP_PREPARE_DYN + 20,
> CPUHP_BRINGUP_CPU,
> CPUHP_AP_IDLE_DEAD,
> CPUHP_AP_OFFLINE,
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index f75c4d031eeb..c47506357519 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1302,10 +1302,24 @@ static int cpuhp_cb_check(enum cpuhp_state state)
> */
> static int cpuhp_reserve_state(enum cpuhp_state state)
> {
> - enum cpuhp_state i;
> + enum cpuhp_state i, end;
> + struct cpuhp_step *step;
>
> - for (i = CPUHP_AP_ONLINE_DYN; i <= CPUHP_AP_ONLINE_DYN_END; i++) {
> - if (!cpuhp_ap_states[i].name)
> + switch (state) {
> + case CPUHP_AP_ONLINE_DYN:
> + step = cpuhp_ap_states + CPUHP_AP_ONLINE_DYN;
> + end = CPUHP_AP_ONLINE_DYN_END;
> + break;
> + case CPUHP_BP_PREPARE_DYN:
> + step = cpuhp_bp_states + CPUHP_BP_PREPARE_DYN;
> + end = CPUHP_BP_PREPARE_DYN_END;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + for (i = state; i <= end; i++, step++) {
> + if (!step->name)
> return i;
> }
> WARN(1, "No more dynamic states available for CPU hotplug\n");
> @@ -1323,7 +1337,7 @@ static int cpuhp_store_callbacks(enum cpuhp_state state,
> const char *name,
>
> mutex_lock(&cpuhp_state_mutex);
>
> - if (state == CPUHP_AP_ONLINE_DYN) {
> + if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) {
> ret = cpuhp_reserve_state(state);
> if (ret < 0)
> goto out;

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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