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sched: core: Minimize number of tasks to load balance

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We don't want sched_nr_migrate to be too high, as that would impact
real-time latencies as the load balancing process for SCHED_OTHER
disallows IRQ interrupts.

Instead of making this a constant value, let's use an amount that
relates to the CPU performance of a device.

Consider that a device with a very weak 4 core processor needs to load
balance 32 tasks from the most busy-but-idle CPU. That balancing would
take significantly longer than a device with 8 cores.

On the contrary view, that same 8 core device balancing 32 tasks would
have no issues with SCHED_OTHER performance, however, real-time tasks
would suffer more jitter than is necessary.

Let's only balance as many tasks as there are CPUs in a device for
optimal SCHED_OTHER performance and SCHED_FIFO / SCHED_RR latency.
This commit is contained in:
Tyler Nijmeh 2024-03-03 13:33:39 +08:00 • committed by Ksawlii
parent a163b49c80
commit e983caf81d
1 changed files with 2 additions and 2 deletions
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4
kernel/sched/core.c
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@ -81,9 +81,9 @@ EXPORT_SYMBOL_GPL(sysctl_sched_features);
* Limited because this is done with IRQs disabled.
*/
#if !defined(CONFIG_ANDROID)
const_debug unsigned int sysctl_sched_nr_migrate = 32;
const_debug unsigned int sysctl_sched_nr_migrate = NR_CPUS;
#else
const_debug unsigned int sysctl_sched_nr_migrate = 32;
const_debug unsigned int sysctl_sched_nr_migrate = NR_CPUS;
#endif
/*