UefiCpuPkg PiSmmCpuDxeSmm: Reduce SMRAM consumption in CpuS3.c

This patch makes two refinements to reduce SMRAM consumption in CpuS3.c.
1. Only do CopyRegisterTable() when register table is not empty,
  IsRegisterTableEmpty() is created to check whether the register table
  is empty or not.

  Take empty PreSmmInitRegisterTable as example, about 24K SMRAM consumption
  could be reduced when mAcpiCpuData.NumberOfCpus=1024.
  sizeof (CPU_REGISTER_TABLE) = 24
  mAcpiCpuData.NumberOfCpus = 1024 = 1K
  mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE) = 24K

2. Only copy table entries buffer instead of whole buffer.
  AllocatedSize in SourceRegisterTableList is the whole buffer size.
  Actually, only the table entries buffer needs to be copied, and the size
  is TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY).

  Take AllocatedSize=0x1000=4096, TableLength=100 and NumberOfCpus=1024 as example,
  about 1696K SMRAM consumption could be reduced.
  sizeof (CPU_REGISTER_TABLE_ENTRY) = 24
  TableLength = 100
  TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY) = 2400
  AllocatedSize = 0x1000 = 4096
  AllocatedSize - TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY) = 4096 - 2400 = 1696
  NumberOfCpus = 1024 = 1K
  NumberOfCpus * (AllocatedSize - TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY)) = 1696K

This patch also corrects the CopyRegisterTable() function description.

Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210111015419.28368-1-star.zeng@intel.com>

0 files changed, 0 insertions, 0 deletions