[patch v3 30/36] x86/smpboot: Enable split CPU startup

Thomas Gleixner
2023-05-08T19:45:56Z

From: Thomas Gleixner <tglx@linutronix.de>

The x86 CPU bringup state currently does AP wake-up, wait for AP to
respond and then release it for full bringup.

It is safe to be split into a wake-up and and a separate wait+release
state.

Provide the required functions and enable the split CPU bringup, which
prepares for parallel bringup, where the bringup of the non-boot CPUs takes
two iterations: One to prepare and wake all APs and the second to wait and
release them. Depending on timing this can eliminate the wait time
completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>

---
arch/x86/Kconfig | 2 +-
arch/x86/include/asm/smp.h | 9 ++-------
arch/x86/kernel/smp.c | 2 +-
arch/x86/kernel/smpboot.c | 8 ++++----
arch/x86/xen/smp_pv.c | 4 ++--
5 files changed, 10 insertions(+), 15 deletions(-)
---

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -274,8 +274,8 @@ config X86
select HAVE_UNSTABLE_SCHED_CLOCK
select HAVE_USER_RETURN_NOTIFIER
select HAVE_GENERIC_VDSO
- select HOTPLUG_CORE_SYNC_FULL if SMP
select HOTPLUG_SMT if SMP
+ select HOTPLUG_SPLIT_STARTUP if SMP
select IRQ_FORCED_THREADING
select NEED_PER_CPU_EMBED_FIRST_CHUNK
select NEED_PER_CPU_PAGE_FIRST_CHUNK
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -40,7 +40,7 @@ struct smp_ops {

void (*cleanup_dead_cpu)(unsigned cpu);
void (*poll_sync_state)(void);
- int (*cpu_up)(unsigned cpu, struct task_struct *tidle);
+ int (*kick_ap_alive)(unsigned cpu, struct task_struct *tidle);
int (*cpu_disable)(void);
void (*cpu_die)(unsigned int cpu);
void (*play_dead)(void);
@@ -80,11 +80,6 @@ static inline void smp_cpus_done(unsigne
smp_ops.smp_cpus_done(max_cpus);
}

-static inline int __cpu_up(unsigned int cpu, struct task_struct *tidle)
-{
- return smp_ops.cpu_up(cpu, tidle);
-}
-
static inline int __cpu_disable(void)
{
return smp_ops.cpu_disable();
@@ -124,7 +119,7 @@ void native_smp_prepare_cpus(unsigned in
void calculate_max_logical_packages(void);
void native_smp_cpus_done(unsigned int max_cpus);
int common_cpu_up(unsigned int cpunum, struct task_struct *tidle);
-int native_cpu_up(unsigned int cpunum, struct task_struct *tidle);
+int native_kick_ap(unsigned int cpu, struct task_struct *tidle);
int native_cpu_disable(void);
void __noreturn hlt_play_dead(void);
void native_play_dead(void);
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -268,7 +268,7 @@ struct smp_ops smp_ops = {
#endif
.smp_send_reschedule = native_smp_send_reschedule,

- .cpu_up = native_cpu_up,
+ .kick_ap_alive = native_kick_ap,
.cpu_disable = native_cpu_disable,
.play_dead = native_play_dead,

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1058,7 +1058,7 @@ static int do_boot_cpu(int apicid, int c
return ret;
}

-static int native_kick_ap(unsigned int cpu, struct task_struct *tidle)
+int native_kick_ap(unsigned int cpu, struct task_struct *tidle)
{
int apicid = apic->cpu_present_to_apicid(cpu);
int err;
@@ -1094,15 +1094,15 @@ static int native_kick_ap(unsigned int c
return err;
}

-int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
+int arch_cpuhp_kick_ap_alive(unsigned int cpu, struct task_struct *tidle)
{
- return native_kick_ap(cpu, tidle);
+ return smp_ops.kick_ap_alive(cpu, tidle);
}

void arch_cpuhp_cleanup_kick_cpu(unsigned int cpu)
{
/* Cleanup possible dangling ends... */
- if (smp_ops.cpu_up == native_cpu_up && x86_platform.legacy.warm_reset)
+ if (smp_ops.kick_ap_alive == native_kick_ap && x86_platform.legacy.warm_reset)
smpboot_restore_warm_reset_vector();
}

--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -314,7 +314,7 @@ cpu_initialize_context(unsigned int cpu,
return 0;
}

-static int xen_pv_cpu_up(unsigned int cpu, struct task_struct *idle)
+static int xen_pv_kick_ap(unsigned int cpu, struct task_struct *idle)
{
int rc;

@@ -438,7 +438,7 @@ static const struct smp_ops xen_smp_ops
.smp_prepare_cpus = xen_pv_smp_prepare_cpus,
.smp_cpus_done = xen_smp_cpus_done,

- .cpu_up = xen_pv_cpu_up,
+ .kick_ap_alive = xen_pv_kick_ap,
.cpu_die = xen_pv_cpu_die,
.cleanup_dead_cpu = xen_pv_cleanup_dead_cpu,
.poll_sync_state = xen_pv_poll_sync_state,