From mboxrd@z Thu Jan 1 00:00:00 1970 From: Preeti U Murthy Subject: Re: [PATCH V2] cpuidle: Handle tick_broadcast_enter() failure gracefully Date: Fri, 08 May 2015 13:06:32 +0530 Message-ID: <554C6780.5050306@linux.vnet.ibm.com> References: <20150507174355.25321.85885.stgit@preeti.in.ibm.com> <1562115.g1s3BW0dJA@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1562115.g1s3BW0dJA@vostro.rjw.lan> Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: peterz@infradead.org, tglx@linutronix.de, rafael.j.wysocki@intel.com, daniel.lezcano@linaro.org, rlippert@google.com, linux-pm@vger.kernel.org, linus.walleij@linaro.org, linux-kernel@vger.kernel.org, mingo@redhat.com, sudeep.holla@arm.com, linuxppc-dev@lists.ozlabs.org List-Id: linux-pm@vger.kernel.org On 05/08/2015 02:20 AM, Rafael J. Wysocki wrote: > On Thursday, May 07, 2015 11:17:21 PM Preeti U Murthy wrote: >> When a CPU has to enter an idle state where tick stops, it makes a call >> to tick_broadcast_enter(). The call will fail if this CPU is the >> broadcast CPU. Today, under such a circumstance, the arch cpuidle code >> handles this CPU. This is not convincing because not only are we not >> aware what the arch cpuidle code does, but we also do not account for >> the idle state residency time and usage of such a CPU. >> >> This scenario can be handled better by simply asking the cpuidle >> governor to choose an idle state where in ticks do not stop. To >> accommodate this change move the setting of runqueue idle state from the >> core to the cpuidle driver, else the rq->idle_state will be set wrong. >> >> Signed-off-by: Preeti U Murthy >> --- >> Changes from V1: https://lkml.org/lkml/2015/5/7/24 >> Rebased on the latest linux-pm/bleeding-edge >> >> drivers/cpuidle/cpuidle.c | 21 +++++++++++++++++---- >> drivers/cpuidle/governors/ladder.c | 13 ++++++++++--- >> drivers/cpuidle/governors/menu.c | 6 +++++- >> include/linux/cpuidle.h | 6 +++--- >> include/linux/sched.h | 16 ++++++++++++++++ >> kernel/sched/core.c | 17 +++++++++++++++++ >> kernel/sched/fair.c | 2 +- >> kernel/sched/idle.c | 8 +------- >> kernel/sched/sched.h | 24 ------------------------ >> 9 files changed, 70 insertions(+), 43 deletions(-) >> >> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c >> index 8c24f95..b7e86f4 100644 >> --- a/drivers/cpuidle/cpuidle.c >> +++ b/drivers/cpuidle/cpuidle.c >> @@ -21,6 +21,7 @@ >> #include >> #include >> #include >> +#include >> #include >> >> #include "cpuidle.h" >> @@ -168,10 +169,17 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, >> * CPU as a broadcast timer, this call may fail if it is not available. >> */ >> if (broadcast && tick_broadcast_enter()) { >> - default_idle_call(); >> - return -EBUSY; >> + index = cpuidle_select(drv, dev, !broadcast); > > No, you can't do that. > > This code path may be used by suspend-to-idle and that should not call > cpuidle_select(). > > What's needed here seems to be a fallback mechanism like "choose the > deepest state shallower than X and such that it won't stop the tick". > You don't really need to run a full governor for that. Agreed. Makes the patch a lot simpler as well. I have sent out V3 doing this. Thank you Regards Preeti U Murthy > >