> -----Original Message----- > From: Daniel Lezcano [mailto:[email protected]] > Sent: Thursday, August 14, 2014 9:30 PM > To: Peter Zijlstra > Cc: Liu, Chuansheng; Rafael J. Wysocki; [email protected]; LKML; Liu, > Changcheng; Wang, Xiaoming; Chakravarty, Souvik K > Subject: Re: [PATCH] cpuidle: Fix the CPU stuck at C0 for 2-3s after PM_QOS > back to DEFAULT
> I think the main issue here is to exit the poll_idle loop when an IPI is > received. IIUC, there is a pm_qos user, perhaps a driver (Chuansheng can > give more details), setting a very short latency, so the cpuidle > framework choose a shallow state like the poll_idle and then the driver > sets a bigger latency, leading to the IPI to wake all the cpus. As the > CPUs are in the poll_idle, they don't exit until an event make them to > exit the need_resched() loop (reschedule or whatever). This situation > can let the CPUs to stand in the infinite loop several seconds while we > are expecting them to exit the poll_idle and enter a deeper idle state, > thus with an extra energy consumption. > Exactly, no function error here. But do not enter the deeper C-state will bring more power consumption, in some mp3 standby mode, even 10% power can be saved. And this is the patch's aim here.
