Re: [edk2-devel] [PATCH 1/5] UefiCpuPkg/MpInitLib: Add ProcessorIndex argument to GetMpHandOffHob()

["Gerd Hoffmann" <kraxel@redhat.com>]

On Mon, Feb 19, 2024 at 02:34:42AM +0000, Ni, Ray wrote:
> > +  for (GuidHob = GetFirstGuidHob (&mMpHandOffGuid);
> > +       GuidHob != NULL;
> > +       GuidHob = GetNextGuidHob (&mMpHandOffGuid, GET_NEXT_HOB
> > (GuidHob)))
> > +  {
> >      MpHandOff = (MP_HAND_OFF *)GET_GUID_HOB_DATA (GuidHob);
> > +    if (MpHandOff->ProcessorIndex == ProcessorIndex) {
> > +      return MpHandOff;
> > +    }
> 
> Gerd,
> The code is doing correctly but I have concerns about the performance impact.
> 
> With the prototype GetMpHandOffHob(), callers call it multiple times to enumerate all HOB instances.
> 
> But every call is a HOB list enumeration from top of the HOB list which may be slow in a platform
> that contains lots of HOB items and the MpHandOff HOB instances happen to be in the very bottom.
> 
> How about add another parameter "HobStart" to GetMpHandOffHob()? So that only the first call to
> GetMpHandOffHob() is a HOB list enumeration from top, latter calls start from the next HOB of the previous
> found MpHandOff HOB instance.

That will only work if the HOBs are returned in ProcessorIndex order.

That happens to be the case in my testing; the HOBs are returned in the
same order they are created by patch #5 of this series.

Is that behavior guaranteed?  MdePkg/Include/Library/HobLib.h doesn't
say anything about the ordering.

take care,
  Gerd



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