On 06/29/2012 09:41 AM, 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.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. >> >>> 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.This means we need to disable > entry into deeper C-states even before dpm_suspend_start(),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. To clarify this further,since we take action upon PM_SUSPEND_PREPARE notification,which is called before suspend begins,we avoid race condition between suspend operations and disabling entry into deeper c-states altogether. >> >> 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? > 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. >> That would be much more deterministic than your patch I think. >> >> Thanks, >> Rafael >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-pm" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > Regards > Preeti > > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html >
