On devices with a CPU that contains heterogeneous cores (e.g.,
big.LITTLE), it can be beneficial to place some performance-critical
IRQs and kthreads onto the performance CPU cluster in order to improve
performance.
This commit adds the following APIs:
-kthread_run_perf_critical() to create and start a perf-critical kthread
-irq_set_perf_affinity() to mark an active IRQ as perf-critical
-IRQF_PERF_CRITICAL to schedule an IRQ and any threads it may have onto
performance CPUs
-PF_PERF_CRITICAL to mark a process (mainly a kthread) as performance
critical (this is used by kthread_run_perf_critical())
In order to accommodate this new API, the following changes are made:
-Performance-critical IRQs are distributed evenly among online CPUs
available in cpu_perf_mask
-Performance-critical IRQs have their affinities reaffined upon exit
from suspend (since the affinities are broken when non-boot CPUs are
disabled)
-Performance-critical IRQs and their threads have their affinities reset
upon entering suspend, so that upon immediate suspend exit (when only
the boot CPU is online), interrupts can be processed and interrupt
threads can be scheduled onto an online CPU (otherwise we'd hit a
kernel BUG)
-__set_cpus_allowed_ptr() is modified to enforce a performance-critical
kthread's affinity
-Perf-critical IRQs are marked with IRQD_AFFINITY_MANAGED so userspace
can't mess with their affinity
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
a1ede341b3