- Reduce the preemption disabled sections in smp_call_function*().
The various smp call functions keep preemption disabled accross the
full operation which includes the wait for completion. Especially the
latter can take some time when one of the target CPUs is not
immediately responding to the IPI, which can result in large latency
spikes.
To improve this provide a per task CPU mask to track the CPUs to wait
for. That makes the information required for the wait task local and
therefore allows to reenable preemption before the wait. While this
comes with moderate extra memory cost this reduces SMP function call
induced latency measured in a fleet for high priority tasks from ~17ms
to ~1.5ms (~90%).
- Reduce the overhead of the CSD debug code by replacing the heavy memory
barriers with smp_store_release()/acquire().
- Remove obsolute unused hotplug states
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Merge tag 'smp-core-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull SMP core updates from Thomas Gleixner:
- Reduce the preemption disabled sections in smp_call_function*().
The various smp call functions keep preemption disabled accross the
full operation which includes the wait for completion. Especially the
latter can take some time when one of the target CPUs is not
immediately responding to the IPI, which can result in large latency
spikes.
To improve this provide a per task CPU mask to track the CPUs to wait
for. That makes the information required for the wait task local and
therefore allows to reenable preemption before the wait.
While this comes with moderate extra memory cost this reduces SMP
function call induced latency measured in a fleet for high priority
tasks from ~17ms to ~1.5ms (~90%).
- Reduce the overhead of the CSD debug code by replacing the heavy
memory barriers with smp_store_release()/acquire()
- Remove obsolute unused hotplug states
* tag 'smp-core-2026-08-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
scftorture: Remove preempt_disable() in scftorture_invoke_one()
smp: Remove preempt_disable() from on_each_cpu_cond_mask()
smp: Remove preempt_disable() from smp_call_function()
smp: Enable preemption early in smp_call_function_many_cond()
smp: Alloc percpu csd data in smpcfd_prepare_cpu() only once
smp: Use task-local IPI cpumask in smp_call_function_many_cond()
smp: Refactor remote CPU selection in smp_call_function_any()
smp: Enable preemption early in smp_call_function_single()
smp: Disable preemption explicitly in __csd_lock_wait()
cpu/hotplug: Remove CPUHP_AP_ARM_CORESIGHT_CTI_STARTING
smp: Use release stores for csd_lock_record() state
0dd1a54f44