On 2015/1/27 23:10, Rafael J. Wysocki wrote: > On Tuesday, January 27, 2015 04:03:29 PM Li, Aubrey wrote: >> On 2015/1/26 22:41, Rafael J. Wysocki wrote: >>> On Monday, January 26, 2015 10:40:24 AM Thomas Gleixner wrote: >>>> On Mon, 26 Jan 2015, Li, Aubrey wrote: >>>>> On 2015/1/22 18:15, Thomas Gleixner wrote: >>> >>> [...] >>> >>>>>>> + /* >>>>>>> + * cpuidle_enter will return with interrupt enabled >>>>>>> + */ >>>>>>> + cpuidle_enter(drv, dev, next_state); >>>>>> >>>>>> How is that supposed to work? >>>>>> >>>>>> If timekeeping is not yet unfrozen, then any interrupt handling code >>>>>> which calls anything time related is going to hit lala land. >>>>>> >>>>>> You must guarantee that timekeeping is unfrozen before any interrupt >>>>>> is handled. If you cannot guarantee that, you cannot freeze >>>>>> timekeeping ever. >>>>>> >>>>>> The cpu local tick device is less critical, but it happens to work by >>>>>> chance, not by design. >>>>> >>>>> There are two way to guarantee this: the first way is, disable interrupt >>>>> before timekeeping frozen and enable interrupt after timekeeping is >>>>> unfrozen. However, we need to handle wakeup handler before unfreeze >>>>> timekeeping to wake freeze task up from wait queue. >>>>> >>>>> So we have to go the other way, the other way is, we ignore time related >>>>> calls during freeze, like what I added in irq_enter below. >>>> >>>> Groan. You just do not call in irq_enter/exit(), but what prevents any >>>> interrupt handler or whatever to call into the time/timer code after >>>> interrupts got reenabled? >>>> >>>> Nothing. >>>> >>>>> Or, we need to re-implement freeze wait and wake up mechanism? >>>> >>>> You need to make sure in the low level idle implementation that this >>>> cannot happen. >>>> >>>> tick_freeze() >>>> { >>>> raw_spin_lock(&tick_freeze_lock); >>>> tick_frozen++; >>>> if (tick_frozen == num_online_cpus()) >>>> timekeeping_suspend(); >>>> else >>>> tick_suspend_local(); >>>> raw_spin_unlock(&tick_freeze_lock); >>>> } >>>> >>>> tick_unfreeze() >>>> { >>>> raw_spin_lock(&tick_freeze_lock); >>>> if (tick_frozen == num_online_cpus()) >>>> timekeeping_resume(); >>>> else >>>> tick_resume_local(); >>>> tick_frozen--; >>>> raw_spin_unlock(&tick_freeze_lock); >>>> } >>>> >>>> idle_freeze() >>>> { >>>> local_irq_disable(); >>>> >>>> tick_freeze(); >>>> >>>> /* Must keep interrupts disabled! */ >>>> go_deep_idle() >>>> >>>> tick_unfreeze(); >>>> >>>> local_irq_enable(); >>>> } >>>> >>>> That's the only way you can do it proper, everything else will just be >>>> a horrible mess of bandaids and duct tape. >>>> >>>> So that does not need any of the irq_enter/exit conditionals, it does >>>> not need the real_handler hack. It just works. >>> >>> As long as go_deep_idle() above does not enable interrupts. This means we >>> won't >>> be able to use some C-states for suspend-to-idle (hald-induced C1 on some >>> x86 >>> for one example), but that's not a very big deal. >> >> Does the legacy ACPI system IO method to enter C2/C3 need interrupt >> enabled as well? >> >> Do we need some platform ops to cover those legacy platforms? Different >> platform go different branch here. > > No, we don't. > > I think this needs to be addressed in a different way overall. If you don't > mind, I'd like to prepare my own version of the patch at this point. That > likely will be simpler than trying to explain what I'd like to do and I guess > I'll need a few iterations to get something acceptable anyway.
Sure, please go ahead and just keep me posted. Thanks, -Aubrey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/