Hi, Some archs allow the system administrator to set the idle thread behavior to spin instead of entering sleep states. The x86 arch, for example, has a idle= command-line parameter for this purpose.
However, the command-line parameter has two problems: 1. You have to reboot if you change your mind 2. This setting affects all system cores The second point is relevant for systems where cores are partitioned into bookkeeping and low-latency cores. Usually, it's OK for bookkeeping cores to enter deeper sleep states. It's only the low-latency cores that should poll when entering idle. This series adds the following file: /sys/devices/system/cpu/cpu_idle This file outputs and stores a cpumask of the cores which will have idle polling behavior. This implementation seems to work fine on x86, however it's RFC because of the following points (for which feedback is greatly appreciated): o I believe this implementation should work for all archs, but I can't confirm it as my machines and experience is limited to x86 o Some x86 cpufreq drivers explicitly check if idle=poll was passed. Does anyone know if this is an optmization or is there actually a conflict between idle=poll and driver operation? o This series maintains cpu_idle_poll_ctrl() semantics which led to a more complex implementation. That is, today cpu_idle_poll_ctrl() increments or decrements a counter. A lot of arch code seems to count on this semantic, where cpu_idle_poll_ctrl(enable or false) calls have to match to enable or disable idle polling Luiz Capitulino (3): sched/idle: cpu_idle_poll(): drop unused return code sched/idle: make cpu_idle_force_poll per-cpu sched/idle: run-time support for setting idle polling drivers/base/cpu.c | 44 ++++++++++++++++++++++++ include/linux/cpu.h | 2 ++ kernel/sched/idle.c | 96 +++++++++++++++++++++++++++++++++++++++++++++-------- 3 files changed, 129 insertions(+), 13 deletions(-) -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
