Messages in this thread | | | From | "Liu, Chuansheng" <> | Subject | RE: [PATCH] cpuidle: Fix the CPU stuck at C0 for 2-3s after PM_QOS back to DEFAULT | Date | Thu, 14 Aug 2014 14:10:27 +0000 |
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> -----Original Message----- > From: Peter Zijlstra [mailto:peterz@infradead.org] > Sent: Thursday, August 14, 2014 9:13 PM > To: Liu, Chuansheng > Cc: Daniel Lezcano; Rafael J. Wysocki; linux-pm@vger.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 > > On Thu, Aug 14, 2014 at 11:24:06AM +0000, Liu, Chuansheng wrote: > > If inspecting the polling flag, we can not fix the race between poll_idle and > smp_callback, > > since in poll_idle(), before set polling flag, if the smp_callback come in, then > no resched bit set, > > after that, poll_idle() will do the polling action, without reselection > immediately, it will bring power > > regression here. > > -ENOPARSE. Is there a question there?
Lezcano suggest to inspect the polling flag, then code is like below: smp_callback() { if (polling_flag) set_resched_bit; }
And the poll_idle code is like below: static int poll_idle(struct cpuidle_device *dev, struct cpuidle_driver *drv, int index) { local_irq_enable(); if (!current_set_polling_and_test()) { while (!need_resched()) cpu_relax(); } current_clr_polling();
return index; }
The race is: Idle task: poll_idle local_irq_enable() <== IPI interrupt coming, check the polling flag is not set yet, do nothing; Come back to poll_idle, it will stay in the poll loop for a while, instead break it immediately to let governor reselect the right C-state.
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