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

["Yao, Jiewen" <jiewen.yao@intel.com>]

Hi
I believe using stack pointer is not a robust way if the stack guard feature is not enabled. Stack pointer may overflow.

Can we use GDT? Each AP has its own GDT.

Thank you
Yao Jiewen


> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Dong,
> Eric
> Sent: Monday, July 9, 2018 2:13 PM
> To: Dong, Eric <eric.dong@intel.com>; 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,
> 
> 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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> > > >
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