Re: Regression in intel_idle on Avaton/Rangely Mohon Peak board

[Paul Gortmaker <paul.gortmaker@windriver.com>]

On 14-04-01 05:59 PM, Brown, Len wrote:
>> I've got an eval board with a 1.7GHz Avaton/C2000 that hangs at boot
>> shortly after the idle driver registration -- typically 1/2 dozen
>> dmesg lines later, around rtc init, or net stack init.
> 
> Paul,
> Please boot the failing board with "intel_idle.max_cstate=0"
> to disable intel_idle entirely, and then show the C-states
> exported by acpi_idle, that predumably, are stable on both boards:
> 
> dmesg | grep idle
> grep . /sys/devices/system/cpu/cpu0/cpuidle/*/*
> 
> Then go back and boot with "intel_idle.max_cstate=N"
> where N is incremented by 1 until when the system fails
> and note the largest N that still works.

The dying board works for N=1, fails for N=2.

root@localhost:/sys/devices/system/cpu/cpuidle# grep . *
current_driver:intel_idle
current_governor_ro:menu
root@localhost:/sys/devices/system/cpu/cpuidle# dmesg|grep idle
[    0.000000] Command line: BOOT_IMAGE=/boot/bzImage-current console=tty0 noinitrd root=/dev/sda4 rw ip=dhcp selinux=0 enforcing=0 intel_idle.max_cstate=1
[    0.000000] Kernel command line: BOOT_IMAGE=/boot/bzImage-current console=tty0 noinitrd root=/dev/sda4 rw ip=dhcp selinux=0 enforcing=0 intel_idle.max_cstate=1
[    0.000000] 	RCU dyntick-idle grace-period acceleration is enabled.
[    0.217203] cpuidle: using governor ladder
[    0.217309] cpuidle: using governor menu
[    0.840598] intel_idle: MWAIT substates: 0x33000020
[    0.840662] intel_idle: v0.4 model 0x4D
[    0.840668] intel_idle: lapic_timer_reliable_states 0x2
[    0.840673] intel_idle: max_cstate 1 reached
root@localhost:/sys/devices/system/cpu/cpuidle#

Another interesting data point -- the dying board doesn't die if
I boot 3.14's x86-64 defconfig.  Nothing immediately jumps out at
me in the dying .config ; there are a few tweaks in there like
RCU_NOCB etc. that I'll have to weed out with a pseudo .config
bisect I guess....

I'll go get the N=1 and N=2 data for the working board next.

Paul.
--

> 
>> The interesting part is that a nearly identical board, but with
>> different (newer/faster) CPU and newer BIOS doesn't have the hang.
> 
> Possibly an electrical bug in the earlier board.
> Maybe they worked around it by disabling a C-state in ACPI
> and didn't test upstream Linux?
> 
> I'd be interested in the acpi_idle output above for both the
> new and old boards to see if they are exporting different states
> on the two boards.
> 
> dmidecode isn't useful in this case.  The CPUID in /proc/cpuinfo
> may be useful if the problem turns out to be associated with
> some stepping.
> 
> thanks,
> -Len
>