Re: [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib: Avoid AP calls PeiService.

[Laszlo Ersek <lersek@redhat.com>]

Hi Eric,

On 01/09/19 06:26, Dong, Eric wrote:
> Hi all,
> 
> We got some feedback about this BZ. Someone think this timeout is valuable for the debug purpose, and oppose to remove it. 
> https://bugzilla.tianocore.org/show_bug.cgi?id=1419
> 
> So I'm back to here and want to still use this change. I not use "update PcdSpinLockTimeout to 0 in platform" solution because I think core driver depends on platform policy is not a good design. 
> 
> Do you guys have any other concern?

sorry, I don't understand.

(1) In <https://bugzilla.tianocore.org/show_bug.cgi?id=1419>, where
currently comment #2 is the last comment, I don't see any request for
keeping the timeout facility.

(2) On the mailing list as well, you seem to have received comments only
in favor of removing the timeout facility.

"Someone think this timeout is valuable for the debug purpose" doesn't
cut it, for open development. I don't care about the identity of the
person that wants to preserve the feature, but I certainly care about
their use case. You shouldn't have to mediate and describe their use
case for them, on the list; that's always a lossy process.

Regarding the PCD: I think zeroing "PcdSpinLockTimeout" to disable the
timeout case is a valid approach, it's just that we should change the
default value in the DEC file to zero. Then the PCD setting will become
a burden only for those platforms and those use cases that want to use
the timeout feature (such as for debugging).

In general, PCD default values in DEC files have to be considered
carefully, but in some cases, such changes are the right thing. Another
example was 509f8425b75d ("UefiCpuPkg: change PcdCpuSmmStackGuard
default to TRUE", 2016-06-06).

(You made the same point at the end of
<https://bugzilla.tianocore.org/show_bug.cgi?id=1419#c2>.)


In addition to changing the default value to zero, I'd suggest moving
"PcdSpinLockTimeout" from section

[PcdsFixedAtBuild,PcdsPatchableInModule]

to section

[PcdsFixedAtBuild, PcdsPatchableInModule, PcdsDynamic, PcdsDynamicEx]

so that platforms can enable the "debug" feature (i.e. set a nonzero
value) more flexibly.

Thanks
Laszlo

>> -----Original Message-----
>> From: Brian J. Johnson [mailto:brian.johnson@hpe.com]
>> Sent: Friday, December 21, 2018 12:36 AM
>> To: Yao, Jiewen <jiewen.yao@intel.com>; Ni, Ruiyu <ruiyu.ni@intel.com>;
>> Dong, Eric <eric.dong@intel.com>; edk2-devel@lists.01.org
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Subject: Re: [edk2] [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib: Avoid
>> AP calls PeiService.
>>
>> Agreed.  We've seen issues on real platforms with timed-out spinlocks in DXE
>> causing calls to GetPerformanceCounter and DebugAssert.  (DXE has the
>> same code, with the same issues.)
>>
>> Note that it's possible to set PcdSpinLockTimeout=0 to work around the issue
>> on a particular platform, or in a particular module.  But if you have to do that
>> for every module which uses APs, and hence could contend for a spinlock, it
>> kind of defeats the point....  We're better off removing the timeout code.
>>
>> Thanks,
>> Brian
>>
>> On 12/19/18 8:08 PM, Yao, Jiewen wrote:
>>> Yes, I agree, if we don't have any real case.
>>>
>>>
>>>> -----Original Message-----
>>>> From: Ni, Ruiyu
>>>> Sent: Thursday, December 20, 2018 10:07 AM
>>>> To: Dong, Eric <eric.dong@intel.com>; Yao, Jiewen
>>>> <jiewen.yao@intel.com>; edk2-devel@lists.01.org
>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>> Subject: RE: [edk2] [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib:
>>>> Avoid AP calls PeiService.
>>>>
>>>> Can you just change the AcquireSpinLock() behavior to remove the
>>>> Timeout PCD consumption?
>>>>
>>>> I haven't seen a real case that the timed acquisition of spin lock is needed.
>>>>
>>>>
>>>> Thanks/Ray
>>>>
>>>>> -----Original Message-----
>>>>> From: Dong, Eric <eric.dong@intel.com>
>>>>> Sent: Thursday, December 20, 2018 9:23 AM
>>>>> To: Yao, Jiewen <jiewen.yao@intel.com>; edk2-devel@lists.01.org
>>>>> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>
>>>>> Subject: RE: [edk2] [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib:
>>>>> Avoid AP calls PeiService.
>>>>>
>>>>>
>>>>> Agreed, Maybe it's time to add a new API like
>>>>> AcquireSpinLockWithoutTimeOut?
>>>>>
>>>>> Thanks,
>>>>> Eric
>>>>>> -----Original Message-----
>>>>>> From: Yao, Jiewen
>>>>>> Sent: Thursday, December 20, 2018 9:19 AM
>>>>>> To: Dong, Eric <eric.dong@intel.com>; edk2-devel@lists.01.org
>>>>>> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Laszlo Ersek
>>>>>> <lersek@redhat.com>
>>>>>> Subject: RE: [edk2] [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib:
>>>>>> Avoid AP calls PeiService.
>>>>>>
>>>>>> Hi
>>>>>> If we think below code is generic, can we have an API for that?
>>>>>>
>>>>>> +      //
>>>>>> +      // Wait for the AP to release the MSR spin lock.
>>>>>> +      //
>>>>>> +      while (!AcquireSpinLockOrFail (&CpuFlags->ConsoleLogLock)) {
>>>>>> +        CpuPause ();
>>>>>> +      }
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On
>>>>>>> Behalf Of Eric Dong
>>>>>>> Sent: Thursday, December 20, 2018 9:16 AM
>>>>>>> To: edk2-devel@lists.01.org
>>>>>>> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Laszlo Ersek
>>>>>>> <lersek@redhat.com>
>>>>>>> Subject: [edk2] [Patch 1/3] UefiCpuPkg/RegisterCpuFeaturesLib:
>>>>>>> Avoid AP calls PeiService.
>>>>>>>
>>>>>>> In AcquireSpinLock function, it calls GetPerformanceCounter which
>>>>>>> final calls PeiService service. This patch avoid to call
>>>>>>> AcquireSpinLock function.
>>>>>>>
>>>>>>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1411
>>>>>>>
>>>>>>> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
>>>>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>>>>> Contributed-under: TianoCore Contribution Agreement 1.1
>>>>>>> Signed-off-by: Eric Dong <eric.dong@intel.com>
>>>>>>> ---
>>>>>>>
>>>>>>> UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.c
>>>>>>> |
>>>>>>> 7
>>>>>>> ++++++-
>>>>>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git
>>>>>>> a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.
>>>>>>> c
>>>>>>> b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.
>>>>>>> c index 624ddee055..a64326239f 100644
>>>>>>> ---
>>>>>>> a/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.
>>>>>>> c
>>>>>>> +++
>>>> b/UefiCpuPkg/Library/RegisterCpuFeaturesLib/CpuFeaturesInitialize.
>>>>>>> +++ c
>>>>>>> @@ -832,7 +832,12 @@ ProgramProcessorRegister (
>>>>>>>       RegisterTableEntry = &RegisterTableEntryHead[Index];
>>>>>>>
>>>>>>>       DEBUG_CODE_BEGIN ();
>>>>>>> -      AcquireSpinLock (&CpuFlags->ConsoleLogLock);
>>>>>>> +      //
>>>>>>> +      // Wait for the AP to release the MSR spin lock.
>>>>>>> +      //
>>>>>>> +      while (!AcquireSpinLockOrFail (&CpuFlags->ConsoleLogLock)) {
>>>>>>> +        CpuPause ();
>>>>>>> +      }
>>>>>>>         ThreadIndex = ApLocation->Package *
>>>> CpuStatus->MaxCoreCount *
>>>>>>> CpuStatus->MaxThreadCount +
>>>>>>>                 ApLocation->Core * CpuStatus->MaxThreadCount +
>>>>>>>                 ApLocation->Thread;
>>>>>>> --
>>>>>>> 2.15.0.windows.1
>>>>>>>
>>>>>>> _______________________________________________
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>>> _______________________________________________
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>>
>>
>> --
>> Brian J. Johnson
>> Enterprise X86 Lab
>>
>> Hewlett Packard Enterprise
>>
>> brian.johnson@hpe.com
>