[PATCH 1/1] arm: kernel: idle loop pm constraints
flat view
From: Russell King - ARM Linux <hidden>
Date: 2010-08-07 14:14:43
On Fri, Aug 06, 2010 at 12:17:41PM +0300, Samu Onkalo wrote:
Check pm qos cpu latency requirements before preparing for pm-idle activities. Scheduling is prevented during those operations and interrupt thread serving latency in increased. Driver can set pm qos latency requirement to zero to indicate extreme tight latency needs.
NAK. This breaks hotplug CPU support.
quoted hunk ↗ jump to hunk
while (1) { + if (pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY) == 0) { + preempt_enable_no_resched(); + schedule(); + preempt_disable(); + continue; + }
It's pointless to repeatedly call schedule() if need_resched() is not set - and the need_resched() check is extremely cheap. In any case, the parts that you're cutting out are the calls to leds_event() down to tick_nohz_restart_sched_tick(). Do you know where the additional latency comes from? Is it the code in the pm_idle() hook?