sched: Interrupt Aware Scheduler

Linux のプロセススケジューラで割込み負荷の高いCPU以外にプロセス(スレッド)*1をスケジューリングするパッチらしい。

The patch avoids CPUs which might be considered interrupt-heavy when
trying to schedule threads (on the push side) in the system. Interrupt
Awareness has only been added into the fair scheduling class.

It does so by, using the following algorithm:

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1) When the interrupt is getting processed, the start and the end times
are noted for the interrupt on a per-cpu basis.

2) On a periodic basis the interrupt load is processed for each run
queue and this is mapped in terms of percentage in a global array. The
interrupt load for a given CPU is also decayed over time, so that the
most recent interrupt load has the biggest contribution in the interrupt
load calculations. This would mean the scheduler will try to avoid CPUs
(if it can) when scheduling threads which have been recently busy with
handling hardware interrupts.

3) Any CPU which lies above the 80th percentile in terms of percentage
interrupt load is considered interrupt-heavy.

4) During idle CPU search from the scheduler perspective this
information is used to skip CPUs if better are available.

5) If none of the CPUs are better in terms of idleness and interrupt
load, then the interrupt-heavy CPU is considered to be the best
available CPU.

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Linux-Kernel Archive: [PATCH 1/2] sched: Interrupt Aware Scheduler