Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [patch 6/6] x86: add c1e aware idle function | Date | Thu, 19 Jun 2008 00:27:39 +0200 |
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On Thursday, 19 of June 2008, Thomas Gleixner wrote: > On Thu, 19 Jun 2008, Rafael J. Wysocki wrote: > > On Wednesday, 18 of June 2008, Thomas Gleixner wrote: > > > On Wed, 18 Jun 2008, Rafael J. Wysocki wrote: > > > > On Wednesday, 18 of June 2008, Pavel Machek wrote: > > > > > On Thu 2008-06-12 10:29:00, Thomas Gleixner wrote: > > > > > > C1E on AMD machines is like C3 but without control from the OS. Up to > > > > > > now we disabled the local apic timer for those machines as it stops > > > > > > when the CPU goes into C1E. This excludes those machines from high > > > > > > resolution timers / dynamic ticks, which hurts especially the X2 based > > > > > > laptops. > > > > > > > > > > > > The current boot time C1E detection has another more serious flaw: > > > > > > some BIOSes do not enable C1E until the ACPI processor module is > > > > > > loaded. This causes systems to stop working after that point. > > > > > > > > > > > > To work nicely with C1E enabled machines we use a separate idle > > > > > > function, which checks on idle entry whether C1E was enabled in the > > > > > > Interrupt Pending Message MSR. This allows us to do timer broadcasting > > > > > > > > > > Entering idle is quite a common operation, and reading MSR is quite > > > > > slow. Is it possible to do better here? > > > > > > > > > > What happens if ACPI BIOS toggles MSR on all cpus *while* we are > > > > > entering idle? This seems inherently racy... > > > > > > Well, on most of the machines we see the C1E bit on the first idle > > > entry either on CPU0 or on CPU1. > > > > > > I know of exactly one machine which has the C1E thing enabled late > > > when the ACPI stuff runs. > > > > > > > Yes, and that fits the picture I'm observing on the nx6325 (see the > > > > "linux-next: Tree for June 13: IO APIC breakage on HP nx6325" thread). > > > > > > Hmm, when is the C1E detected on current mainline ? Does the boot CPU > > > have it or is it when the second CPU comes up ? > > > > How can I check that? > > When the boot cpu has it then it prints: > > "Disabling APIC timer"
It does that.
> when the secondary CPU has it then it prints: > > "AMD C1E detected late. Force timer broadcast." > > Current mainline does not check for the late ACPI case so I'm pretty > sure that on your box it is detected during early boot way before we > can switch to highres/dyntick.
Yes, that's the case.
Thanks, Rafael
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