Messages in this thread | | | Date | Thu, 14 Aug 2014 13:00:40 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] cpuidle: Fix the CPU stuck at C0 for 2-3s after PM_QOS back to DEFAULT |
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On Thu, Aug 14, 2014 at 12:29:32PM +0200, Daniel Lezcano wrote: > Hi Chuansheng, > > On 14 August 2014 04:11, Chuansheng Liu <chuansheng.liu@intel.com> wrote: > > > We found sometimes even after we let PM_QOS back to DEFAULT, > > the CPU still stuck at C0 for 2-3s, don't do the new suitable C-state > > selection immediately after received the IPI interrupt. > > > > The code model is simply like below: > > { > > pm_qos_update_request(&pm_qos, C1 - 1); > > < == Here keep all cores at C0 > > ...; > > pm_qos_update_request(&pm_qos, PM_QOS_DEFAULT_VALUE); > > < == Here some cores still stuck at C0 for 2-3s > > } > > > > The reason is when pm_qos come back to DEFAULT, there is IPI interrupt to > > wake up the core, but when core is in poll idle state, the IPI interrupt > > can not break the polling loop.
So seeing how you're from @intel.com I'm assuming you're using x86 here.
I'm not seeing how this can be possible, MWAIT is interrupted by IPIs just fine, which means we'll fall out of the cpuidle_enter(), which means we'll cpuidle_reflect(), and then leave cpuidle_idle_call().
It will indeed not leave the cpu_idle_loop() function and go right back into cpuidle_idle_call(), but that will then call cpuidle_select() which should pick a new C state.
So the interrupt _should_ work. If it doesn't you need to explain why. [unhandled content-type:application/pgp-signature] | |