Native preemption is the culprit [was Re: today's CURRENT lockups]

[Kenneth Culver]

Quoting Jon Noack <noackjr at alumni.rice.edu>:

> On 07/09/04 13:06, Steve Kargl wrote:
>> On Fri, Jul 09, 2004 at 12:53:53PM -0500, Jon Noack wrote:
>>> On 07/09/04 12:25, Steve Kargl wrote:
>>>> On Fri, Jul 09, 2004 at 12:19:09PM -0500, Jon Noack wrote:
>>>>> On 07/09/04 12:15, John Baldwin wrote:
>>>>>> My test machine is not a true SMP machine either, just HTT.
>>>>>> It has been running a -j 256 worldloop overnight with no
>>>>>> problems, so I committed a slightly modified version of the
>>>>>> patch yesterday.
>>>>>
>>>>> Did you test with a UP kernel?  After your latest commit I have
>>>>>  been experiencing regular hard locks on my pre-HTT P4 machine.
>>>>>  Backing out rev. 1.114 of sched_ule.c fixes it.  See my
>>>>> previous message (Re: FreeBSD keeps hanging......): 
>>>>> http://docs.freebsd.org/cgi/mid.cgi?40EECC49.3070501
>>>>
>>>> I've tested it on a UP kernel (HTT enabled, ACPI disabled, APIC 
>>>> enabled, ULE).   Appears to work fine.
>>>
>>> Perhaps it's just extraneous information, but if it's really a UP
>>> kernel (as in, no 'options SMP') then whether you have HTT enabled
>>> doesn't matter at all -- the kernel won't use it.
>>
>> Yes, I know. :-)  I'm just reporting what dmesg tells me about the
>> CPU.
>>
>> CPU: Mobile Intel(R) Pentium(R) 4 - M CPU 2.00GHz (1994.12-MHz
>> 686-class CPU) Origin = "GenuineIntel"  Id = 0xf27  Stepping = 7 
>> Features=0xbfebf9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
>
> Mine also lists HTT, but doesn't actually support it:
> CPU: Intel(R) Pentium(R) 4 CPU 2.53GHz (2539.10-MHz 686-class CPU)
>    Origin = "GenuineIntel"  Id = 0xf24  Stepping = 4
>
> Features=0x3febfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM>
>
> I remember a discussion about this a long time ago, but don't remember
> the details.  Regardless, the flag doesn't actually mean the processor
> supports HTT.
>
> Jon

I was under the impression that all P4's support HTT, but a lot of 
bioses don't
allow users to enable it.

Ken