CPU time accounting broken on 8-STABLE machine after a few hours of uptime

[Andriy Gapon]

on 30/09/2010 02:27 Don Lewis said the following:
> On 29 Sep, Andriy Gapon wrote:
>> on 29/09/2010 11:56 Don Lewis said the following:
>>> I'm using the same kernel config as the one on a slower !SMP box which
>>> I'm trying to squeeze as much performance out of as possible.  My kernel
>>> config file contains these statements:
>>> 	nooptions       SMP
>>> 	nodevice        apic
>>>
>>> Testing with an SMP kernel is on my TODO list.
>>
>> SMP or not, it's really weird to see apic disabled nowadays.
> 
> I tried enabling apic and got worse results.  I saw ping RTTs as high as
> 67 seconds.  Here's the timer info with apic enabled:

I didn't expect anything to change in this output with APIC enabled.

> # sysctl kern.timecounter
> kern.timecounter.tick: 1
> kern.timecounter.choice: TSC(800) ACPI-fast(1000) i8254(0) dummy(-1000000)
> kern.timecounter.hardware: ACPI-fast
> kern.timecounter.stepwarnings: 0
> kern.timecounter.tc.i8254.mask: 65535
> kern.timecounter.tc.i8254.counter: 53633
> kern.timecounter.tc.i8254.frequency: 1193182
> kern.timecounter.tc.i8254.quality: 0
> kern.timecounter.tc.ACPI-fast.mask: 16777215
> kern.timecounter.tc.ACPI-fast.counter: 7988816
> kern.timecounter.tc.ACPI-fast.frequency: 3579545
> kern.timecounter.tc.ACPI-fast.quality: 1000
> kern.timecounter.tc.TSC.mask: 4294967295
> kern.timecounter.tc.TSC.counter: 1341917999
> kern.timecounter.tc.TSC.frequency: 2500014018
> kern.timecounter.tc.TSC.quality: 800
> kern.timecounter.invariant_tsc: 0
> 
> Here's the verbose boot info with apic:
> <http://people.freebsd.org/~truckman/AN-M2_HD-8.1-STABLE-apic-verbose.txt>

vmstat -i ?

> I've also experimented with SMP as well as SCHED_4BSD (all previous
> testing was with !SMP and SCHED_ULE).  I still see occasional problems
> with SCHED_4BSD and !SMP, but so far I have not seen any problems with
> SCHED_ULE and SMP.

Good!

> I did manage to catch the problem with lock profiling enabled:
> <http://people.freebsd.org/~truckman/AN-M2_HD-8.1-STABLE_lock_profile_freeze.txt>
> I'm currently testing SMP some more to verify if it really avoids this
> problem.

OK.

-- 
Andriy Gapon