Re: 答复: [Patch] UefiCpuPkg/MpInitLib: Optimize get processor number performance.

["Dong, Eric" <eric.dong@intel.com>]

Hi Laszlo,

I have created https://bugzilla.tianocore.org/show_bug.cgi?id=1002 to request to add AsmReadEsp() / AsmReadRsp().

Thanks,
Eric

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Dong, Eric
> Sent: Monday, July 9, 2018 11:04 AM
> To: Laszlo Ersek <lersek@redhat.com>; Fan Jeff <vanjeff_919@hotmail.com>;
> edk2-devel@lists.01.org
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>
> Subject: Re: [edk2] 答复: [Patch] UefiCpuPkg/MpInitLib: Optimize get
> processor number performance.
> 
> Hi Laszlo,
> 
> > -----Original Message-----
> > From: Laszlo Ersek [mailto:lersek@redhat.com]
> > Sent: Thursday, July 5, 2018 9:04 PM
> > To: Fan Jeff <vanjeff_919@hotmail.com>; Dong, Eric
> > <eric.dong@intel.com>; edk2-devel@lists.01.org
> > Cc: Ni, Ruiyu <ruiyu.ni@intel.com>
> > Subject: Re: [edk2] 答复: [Patch] UefiCpuPkg/MpInitLib: Optimize get
> > processor number performance.
> >
> > Hi Jeff,
> >
> > On 07/04/18 11:39, Fan Jeff wrote:
> > > Eric,
> > >
> > > Current implementation does not call GetApicid() many times,  Please
> > correct you commit message. Your fix is to improve the performance
> > against the current implementation.
> >
> > I think the original commit message does make sense. Without the
> > patch,
> > GetProcessorNumber() may call GetApicId() up to TotalProcessorNumber
> > times. With the patch, even if we skip the stack range search,
> > GetProcessorNumber() will call GetApicId() just once.
> >
> > [...]
> >
> > Some more questions below, for the patch:
> >
> > > 发件人: Eric Dong <eric.dong@intel.com>
> > > 发送时间: Wednesday, July 4, 2018 4:37:36 PM
> > > 收件人: edk2-devel@lists.01.org
> > > 抄送: Ruiyu Ni; Jeff Fan; Laszlo Ersek
> > > 主题: [Patch] UefiCpuPkg/MpInitLib: Optimize get processor number
> > performance.
> > >
> > > Current function has low performance because it calls GetApicId many
> > > times.
> > >
> > > New logic first try to base on the stack range used by AP to find
> > > the processor number. If this solution failed, then call GetApicId
> > > once and base on this value to search the processor.
> > >
> > > Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> > > Cc: Jeff Fan <vanjeff_919@hotmail.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/MpInitLib/MpLib.c | 25 ++++++++++++++++++++++---
> > >  1 file changed, 22 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > index eb2765910c..abd65bee1a 100644
> > > --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> > > @@ -418,7 +418,8 @@ ApInitializeSync (  }
> > >
> > >  /**
> > > -  Find the current Processor number by APIC ID.
> > > +  First try to find the current Processor number by stack address,
> > > + if it failed, then base on APIC ID.
> > >
> > >    @param[in]  CpuMpData         Pointer to PEI CPU MP Data
> > >    @param[out] ProcessorNumber   Return the pocessor number found
> > > @@ -435,16 +436,34 @@ GetProcessorNumber (
> > >    UINTN                   TotalProcessorNumber;
> > >    UINTN                   Index;
> > >    CPU_INFO_IN_HOB         *CpuInfoInHob;
> > > +  UINT32                  CurrentApicId;
> > >
> > > +  TotalProcessorNumber = CpuMpData->CpuCount;
> > >    CpuInfoInHob = (CPU_INFO_IN_HOB *) (UINTN) CpuMpData-
> > >CpuInfoInHob;
> > >
> > > -  TotalProcessorNumber = CpuMpData->CpuCount;
> > > +  //
> > > +  // First try to base on current stack address to find the AP index.
> > > +  // &TotalProcessorNumber value located in the stack range.
> > > +  //
> > >    for (Index = 0; Index < TotalProcessorNumber; Index ++) {
> > > -    if (CpuInfoInHob[Index].ApicId == GetApicId ()) {
> > > +    if ((CpuInfoInHob[Index].ApTopOfStack > (UINTN)
> > (&TotalProcessorNumber)) &&
> > > +        (CpuInfoInHob[Index].ApTopOfStack -
> > > + CpuMpData->CpuApStackSize < (UINTN) (&TotalProcessorNumber))) {
> > >        *ProcessorNumber = Index;
> > >        return EFI_SUCCESS;
> > >      }
> > >    }
> >
> > (1) If I understand correctly, ApTopOfStack is the exclusive end
> > (highest
> > address) of the AP stack, so any local variable is supposed to start
> > strictly below it (the stack grows down). This seems to justify the
> > ">" relational operator, in the first subcondition; OK.
> >
> > However, what guarantees that the TotalProcessorNumber local variable
> > is not located exactly at the (inclusive) base of the AP stack? IOW, why is "<"
> > correct, in the second subcondition, rather than "<="?
> >
> 
> [Eric]  TotalProcessorNumber is the first local variable in this function, also
> exist other local variables in this function, so I just use "<" here.
> 
> >
> > (2) I'm generally unhappy about taking the address of local variables,
> > in order to determine stack location in C language. Instead, I think
> > we should have
> > AsmReadEsp() / AsmReadRsp() functions -- we used to have
> > AsmReadSp() for Itanium. Please see the following sub-thread, where
> > Jordan originally suggested AsmReadEsp() / AsmReadRsp():
> >
> > http://mid.mail-
> > archive.com/151056410867.15809.659701894226687543@jljusten-skl
> >
> > http://mid.mail-
> > archive.com/151059627258.20614.16505766191415005802@jljusten-skl
> >
> > Should I file a Feature Request for BaseLib, about adding AsmReadEsp()
> > / AsmReadRsp()?
> >
> > I'm not suggesting that we block this patch with that feature request,
> > but perhaps we should block the *next* patch.
> >
> 
> [Eric] Yes, I tries to use the function you suggested but we don't find it, so I
> use local variable here.  I agree with your suggest that we should add this API
> for later usage. I will follow up to add this new API and update this patch to V2.
> 
> >
> > For the present patch, I'll follow up with test results separately.
> >
> > Thanks,
> > Laszlo
> >
> > > +
> > > +  //
> > > +  // If can't base on stack to find the AP index, use the APIC ID.
> > > +  //
> > > +  CurrentApicId = GetApicId ();
> > > +  for (Index = 0; Index < TotalProcessorNumber; Index ++) {
> > > +    if (CpuInfoInHob[Index].ApicId == CurrentApicId) {
> > > +      *ProcessorNumber = Index;
> > > +      return EFI_SUCCESS;
> > > +    }
> > > +  }
> > > +
> > >    return EFI_NOT_FOUND;
> > >  }
> > >
> > > --
> > > 2.15.0.windows.1
> > >
> > > _______________________________________________
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> > > edk2-devel@lists.01.org
> > > https://lists.01.org/mailman/listinfo/edk2-devel
> > >
> 
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