[edk2-devel] On RPi4 and Juno, gBS->Stall(1) takes 10us and 100us respectively

[Andrew Fish via groups.io]

Rebecca, 

gBS->Stall() is built on top [1] of the Metronome Architectural Protocol [2]. You should look at how the platform implements the Metronome Architectural Protocol. 

It looks like most platform implement a generic Metronome Driver[3] that just sits on top of the platforms TimerLib [4] implementation. 

You can find the TimerLib implementations via:
$ git grep TimerLib -- \*.inf | grep LIBRARY_CLASS        
ArmPkg/Library/ArmArchTimerLib/ArmArchTimerLib.inf:14:  LIBRARY_CLASS                  = TimerLib
EmbeddedPkg/Library/DebugAgentTimerLibNull/DebugAgentTimerLibNull.inf:19:  LIBRARY_CLASS                  = DebugAgentTimerLib|SEC BASE DXE_CORE
EmulatorPkg/Library/DxeCoreTimerLib/DxeCoreTimerLib.inf:22:  LIBRARY_CLASS                  = TimerLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_DRIVER UEFI_APPLICATION
EmulatorPkg/Library/DxeTimerLib/DxeTimerLib.inf:22:  LIBRARY_CLASS                  = TimerLib|DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_DRIVER UEFI_APPLICATION
EmulatorPkg/Library/PeiTimerLib/PeiTimerLib.inf:22:  LIBRARY_CLASS                  = TimerLib|PEIM PEI_CORE SEC
MdePkg/Library/BaseTimerLibNullTemplate/BaseTimerLibNullTemplate.inf:23:  LIBRARY_CLASS                  = TimerLib
MdePkg/Library/SecPeiDxeTimerLibCpu/SecPeiDxeTimerLibCpu.inf:30:  LIBRARY_CLASS                  = TimerLib
OvmfPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf:17:  LIBRARY_CLASS  = TimerLib|PEI_CORE PEIM DXE_CORE
OvmfPkg/Library/AcpiTimerLib/BaseAcpiTimerLibBhyve.inf:18:  LIBRARY_CLASS  = TimerLib
OvmfPkg/Library/AcpiTimerLib/BaseRomAcpiTimerLib.inf:16:  LIBRARY_CLASS  = TimerLib|SEC
OvmfPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf:17:  LIBRARY_CLASS  = TimerLib|DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_DRIVER UEFI_APPLICATION SMM_CORE
PcAtChipsetPkg/Library/AcpiTimerLib/BaseAcpiTimerLib.inf:21:  LIBRARY_CLASS                  = TimerLib|SEC PEI_CORE PEIM
PcAtChipsetPkg/Library/AcpiTimerLib/DxeAcpiTimerLib.inf:21:  LIBRARY_CLASS                  = TimerLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_APPLICATION UEFI_DRIVER SMM_CORE
PcAtChipsetPkg/Library/AcpiTimerLib/PeiAcpiTimerLib.inf:21:  LIBRARY_CLASS                  = TimerLib|PEI_CORE PEIM
PcAtChipsetPkg/Library/AcpiTimerLib/StandaloneMmAcpiTimerLib.inf:23:  LIBRARY_CLASS                  = TimerLib|MM_CORE_STANDALONE MM_STANDALONE
UefiCpuPkg/Library/CpuTimerLib/BaseCpuTimerLib.inf:18:  LIBRARY_CLASS                  = TimerLib
UefiCpuPkg/Library/SecPeiDxeTimerLibUefiCpu/SecPeiDxeTimerLibUefiCpu.inf:30:  LIBRARY_CLASS                  = TimerLib
UefiPayloadPkg/Library/AcpiTimerLib/AcpiTimerLib.inf:15:  LIBRARY_CLASS                  = TimerLib

So I’d guess your platform is using the ArmArchTimerLi [5]. If that is the case I’d look at the value of PcdArmArchTimerFreqInHz if it is zero then I think you are running on the default ARM timer value. 

If you are using the stock stuff and all your TimerLib instances are the same in all your drivers then the TimerLib is also abstraction the performance measure.

This is probably not helpful but the UEFI Spec defines that Stall() delays for at least the requested amount of time, with no upper bound on how long it can take.  

[1] https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Misc/Stall.c#L49
[2] https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/Metronome.h#L25
[3] https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Universal/Metronome/Metronome.c#L61 
[4] https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Library/TimerLib.h 
[5] https://github.com/tianocore/edk2/blob/master/ArmPkg/Library/ArmArchTimerLib/ArmArchTimerLib.c#L18

Thanks,

Andrew Fish


> On Nov 28, 2022, at 11:02 AM, Rebecca Cran <quic_rcran at quicinc.com> wrote:
> 
> I've been doing some work on USB and ended up realizing that gBS->Stall(1) is taking much longer than it should: on my Juno R2 it's stalling for 100 us, while on my Raspberry Pi 4 it's 10 us.
> 
> This appears to be causing a USB bulk transfer request that asks for a 1ms timeout taking 100ms on the Juno.
> 
> I'm measuring the delay with the following code:
> 
> 
> UINT64 First = GetPerformanceCounter ();
> 
> gBS->Stall (XHC_1_MICROSECOND);
> 
> UINT64 Second = GetPerformanceCounter ();
> 
> UINT64 FirstNs = GetTimeInNanoSecond (First);
> UINT64 SecondNs = GetTimeInNanoSecond (Second);
> 
> DEBUG ((DEBUG_INFO, "Stalled for %llu ns (%llu ms)\n", (SecondNs - FirstNs), (SecondNs - FirstNs) / 1024 / 1024));
> 
> 
> 
> I see output such as:
> 
> Stalled for 10500 ns (0 ms)
> 
> 
> -- 
> Rebecca Cran
> 
> 
> 
> 
> 



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