On Friday, June 29, 2012, preeti wrote: > On 06/29/2012 12:41 AM, Rafael J. Wysocki wrote: > > On Thursday, June 28, 2012, preeti wrote: > >> On 06/28/2012 03:23 PM, Rafael J. Wysocki wrote: > >>> On Thursday, June 28, 2012, preeti wrote: > >>>> > >>>> From: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx> > > [...] > >> cpuidle is an architecture independent part of the kernel code.Since > >> this patch aims at x86 architecture in specific,I considered it > >> inappropriate. > >> > >> In addition to this,suspend happens on x86 only if ACPI is configured. > > > > But that is not required for intel_idle, so if it hangs with intel_idle, > > then it is not dependent on ACPI after all. > True intel_idle does not need ACPI to be configured,but that also means > that the kernel will not provide you the means to suspend. Yes, it will. You can hibernate without ACPI in theory. > There is no question of resume hang here at all as you cannot suspend in > the first place. > > The issue is when ACPI is configured,and intel_idle is chosen to be the > cpuidle driver.In this situation when the user suspends,cpus can enter > deep sleep states as intel_idle driver does not prevent then from doing so. > This is when resume hangs. I know that. > >> Therefore it seemed right to put the callback in ACPI specific code > >> which deals with ACPI sleep support. > > > > I wonder if we can address this issue correctly. That is, in a non-racy > > way and in a better place. > > > > First, I really don't think it is necessary to "suspend" cpuidle (be it > > ACPI or any other) when device drivers' suspend routines are being > > executed (which also is racy, because the cpuidle "suspend" may be running > > concurrently with cpuidle on another CPU) or earlier. We really may want > > to disable the deeper C-states when we're about to execute > > suspend_ops->prepare_late(), or hibernation_ops->prepare(), i.e. after > > we've run dpm_suspend_end() successfully. > > The commit "ACPI:disable lower idle C-states across suspend/resume" > states that device_suspend() calls ACPI suspend functions which cause > side effects on the lower idle C-states. I'd like to know the details, then. Which ACPI suspend functions those are, in particular, because I'm not aware of any in device_suspend(). Also, please note that this commit is 5 years old and some things have changed in the suspend code paths since that time. > This means we need to disable entry into deeper C-states even before > dpm_suspend_start(), This most likely is wrong. We may need to "suspend" cpuidle before calling suspend_device_irqs(), but then again that shouldn't be made via a notifier I think. Why don't we simply make suspend_device_irqs() disable lower C-states to start with? > but how much before? > > The commit answers this too.It says removing the functionality of > entering deep C-states before suspend removed the side effects.Besides, > the commit title says'across suspend/resume'.So I think to address the > resume hang effectively,it is desirable to disable entry into deeper > C-states during suspend_prepare operations. > > > > So, it seems, it might be a good idea to place a cpuidle driver suspend > > (and/or hibernation) hook at the end of dpm_suspend_end() and make ACPI > > and intel_idle drivers implement that hook. > > > Dont you think this patch is meant to fix a very ACPI specific problem? No, I don't. > Which is why I think the call backs or any hook meant to fix this should > go into ACPI specific code. > Else it will seem irrelevant to all other architectures that implement > suspend. I don't honestly think it is irrelevant. The fact is that similar problems have not been reported on other architectures _yet_, which by no means can be taken as a proof that those architectures are not affected. Anyway, I think that the right way to address this is through a cpuidle driver callback executed from suspend_device_irqs() (and analogously for the resume code path) and not through some hacky-ugly ACPI changes. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
