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Message-ID: <27240C0AC20F114CBF8149A2696CBE4A01E5B70B@SHSMSX101.ccr.corp.intel.com> Date: Thu, 14 Aug 2014 13:57:49 +0000 From: "Liu, Chuansheng" <chuansheng.liu@...el.com> To: Daniel Lezcano <daniel.lezcano@...aro.org>, Peter Zijlstra <peterz@...radead.org> CC: "Rafael J. Wysocki" <rjw@...ysocki.net>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, "Liu, Changcheng" <changcheng.liu@...el.com>, "Wang, Xiaoming" <xiaoming.wang@...el.com>, "Chakravarty, Souvik K" <souvik.k.chakravarty@...el.com> Subject: RE: [PATCH] cpuidle: Fix the CPU stuck at C0 for 2-3s after PM_QOS back to DEFAULT > -----Original Message----- > From: Daniel Lezcano [mailto:daniel.lezcano@...aro.org] > Sent: Thursday, August 14, 2014 9:30 PM > To: Peter Zijlstra > Cc: Liu, Chuansheng; Rafael J. Wysocki; linux-pm@...r.kernel.org; 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.
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