On Thu, Aug 14, 2014 at 12:29:32PM +0200, Daniel Lezcano wrote: > Hi Chuansheng, > > On 14 August 2014 04:11, Chuansheng Liu <[email protected]> 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 here in the IPI callback interrupt, when currently the idle task is > > running, we need to forcedly set reschedule bit to break the polling loop, > > as for other non-polling idle state, IPI interrupt can break them directly, > > and setting reschedule bit has no harm for them too. > > > > With this fix, we saved about 30mV power in our android platform. > > > > Signed-off-by: Chuansheng Liu <[email protected]> > > --- > > drivers/cpuidle/cpuidle.c | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c > > index ee9df5e..9e28a13 100644 > > --- a/drivers/cpuidle/cpuidle.c > > +++ b/drivers/cpuidle/cpuidle.c > > @@ -532,7 +532,13 @@ EXPORT_SYMBOL_GPL(cpuidle_register); > > > > static void smp_callback(void *v) > > { > > - /* we already woke the CPU up, nothing more to do */ > > + /* we already woke the CPU up, and when the corresponding > > + * CPU is at polling idle state, we need to set the sched > > + * bit to trigger reselect the new suitable C-state, it > > + * will be helpful for power. > > + */ > > + if (is_idle_task(current)) > > + set_tsk_need_resched(current); > > > > Mmh, shouldn't we inspect the polling flag instead ? Peter (Cc'ed) did some > changes around this and I think we should ask its opinion. I am not sure > this code won't make all cpu to return to the scheduler and go back to the > idle task.
Yes, this is wrong.. Also cpuidle should not know about this, so this is very much the wrong place to go fix this. Lemme have a look.
pgp1JYPQyAXZz.pgp
Description: PGP signature
