[patch 13/37] x86/smpboot: Remove cpu_callin_mask

Thomas Gleixner
2023-04-14T23:45:33Z

Now that TSC synchronization is SMP function call based there is no reason
to wait for the AP to be set in smp_callin_mask. The control CPU waits for
the AP to set itself in the online mask anyway.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/smpboot.c | 61 +++++++---------------------------------------
1 file changed, 10 insertions(+), 51 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -104,7 +104,6 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
/* All of these masks are initialized in setup_cpu_local_masks() */
static cpumask_var_t cpu_initialized_mask;
static cpumask_var_t cpu_callout_mask;
-static cpumask_var_t cpu_callin_mask;
/* Representing CPUs for which sibling maps can be computed */
static cpumask_var_t cpu_sibling_setup_mask;

@@ -167,21 +166,16 @@ static inline void smpboot_restore_warm_
*/
static void smp_callin(void)
{
- int cpuid;
+ int cpuid = smp_processor_id();

/*
* If waken up by an INIT in an 82489DX configuration
- * cpu_callout_mask guarantees we don't get here before
- * an INIT_deassert IPI reaches our local APIC, so it is
- * now safe to touch our local APIC.
- */
- cpuid = smp_processor_id();
-
- /*
- * the boot CPU has finished the init stage and is spinning
- * on callin_map until we finish. We are free to set up this
- * CPU, first the APIC. (this is probably redundant on most
- * boards)
+ * cpu_callout_mask guarantees we don't get here before an
+ * INIT_deassert IPI reaches our local APIC, so it is now safe to
+ * touch our local APIC.
+ *
+ * Set up this CPU, first the APIC, which is probably redundant on
+ * most boards.
*/
apic_ap_setup();

@@ -192,7 +186,7 @@ static void smp_callin(void)
* The topology information must be up to date before
* calibrate_delay() and notify_cpu_starting().
*/
- set_cpu_sibling_map(raw_smp_processor_id());
+ set_cpu_sibling_map(cpuid);

ap_init_aperfmperf();

@@ -205,11 +199,6 @@ static void smp_callin(void)
* state (CPUHP_ONLINE in the case of serial bringup).
*/
notify_cpu_starting(cpuid);
-
- /*
- * Allow the master to continue.
- */
- cpumask_set_cpu(cpuid, cpu_callin_mask);
}

static void ap_calibrate_delay(void)
@@ -268,11 +257,6 @@ static void notrace start_secondary(void
rcu_cpu_starting(raw_smp_processor_id());
x86_cpuinit.early_percpu_clock_init();

- /*
- * Sync point with wait_cpu_callin(). The AP doesn't wait here
- * but just sets the bit to let the controlling CPU (BSP) know that
- * it's got this far.
- */
smp_callin();

/* Otherwise gcc will move up smp_processor_id() before cpu_init() */
@@ -1112,7 +1096,7 @@ static int wait_cpu_cpumask(unsigned int
* and thus wait_for_master_cpu(), then set cpu_callout_mask to allow it
* to proceed. The AP will then proceed past setting its 'callin' bit
* and end up waiting in check_tsc_sync_target() until we reach
- * do_wait_cpu_online() to tend to it.
+ * wait_cpu_online() to tend to it.
*/
static int wait_cpu_initialized(unsigned int cpu)
{
@@ -1127,20 +1111,7 @@ static int wait_cpu_initialized(unsigned
}

/*
- * Bringup step three: Wait for the target AP to reach smp_callin().
- * The AP is not waiting for us here so we don't need to parallelise
- * this step. Not entirely clear why we care about this, since we just
- * proceed directly to TSC synchronization which is the next sync
- * point with the AP anyway.
- */
-static void wait_cpu_callin(unsigned int cpu)
-{
- while (!cpumask_test_cpu(cpu, cpu_callin_mask))
- schedule();
-}
-
-/*
- * Bringup step four: Wait for the target AP to reach set_cpu_online() in
+ * Bringup step three: Wait for the target AP to reach set_cpu_online() in
* start_secondary().
*/
static void wait_cpu_online(unsigned int cpu)
@@ -1170,14 +1141,6 @@ static int native_kick_ap(unsigned int c
}

/*
- * Already booted CPU?
- */
- if (cpumask_test_cpu(cpu, cpu_callin_mask)) {
- pr_debug("do_boot_cpu %d Already started\n", cpu);
- return -ENOSYS;
- }
-
- /*
* Save current MTRR state in case it was changed since early boot
* (e.g. by the ACPI SMI) to initialize new CPUs with MTRRs in sync:
*/
@@ -1214,7 +1177,6 @@ int native_cpu_up(unsigned int cpu, stru
if (ret)
goto out;

- wait_cpu_callin(cpu);
wait_cpu_online(cpu);

out:
@@ -1330,7 +1292,6 @@ void __init smp_prepare_cpus_common(void
* Setup boot CPU information
*/
smp_store_boot_cpu_info(); /* Final full version of the data */
- cpumask_copy(cpu_callin_mask, cpumask_of(0));
mb();

for_each_possible_cpu(i) {
@@ -1545,7 +1506,6 @@ early_param("possible_cpus", _setup_poss
void __init setup_cpu_local_masks(void)
{
alloc_bootmem_cpumask_var(&cpu_initialized_mask);
- alloc_bootmem_cpumask_var(&cpu_callin_mask);
alloc_bootmem_cpumask_var(&cpu_callout_mask);
alloc_bootmem_cpumask_var(&cpu_sibling_setup_mask);
}
@@ -1609,7 +1569,6 @@ static void remove_cpu_from_maps(int cpu
{
set_cpu_online(cpu, false);
cpumask_clear_cpu(cpu, cpu_callout_mask);
- cpumask_clear_cpu(cpu, cpu_callin_mask);
/* was set by cpu_init() */
cpumask_clear_cpu(cpu, cpu_initialized_mask);
numa_remove_cpu(cpu);