lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <27240C0AC20F114CBF8149A2696CBE4A01E5B61C@SHSMSX101.ccr.corp.intel.com> Date: Thu, 14 Aug 2014 11:24:06 +0000 From: "Liu, Chuansheng" <chuansheng.liu@...el.com> To: Peter Zijlstra <peterz@...radead.org>, Daniel Lezcano <daniel.lezcano@...aro.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: Peter Zijlstra [mailto:peterz@...radead.org] > Sent: Thursday, August 14, 2014 6:54 PM > To: Daniel Lezcano > 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 > > 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@...el.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 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 <chuansheng.liu@...el.com> > > > --- > > > 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. 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists