[edk2-devel] [PATCH 7/8] OvmfPkg: disable list length checks in NOOPT and DEBUG builds

[Laszlo Ersek]

In NOOPT and DEBUG builds, if "PcdMaximumLinkedListLength" is nonzero,
then several LIST_ENTRY *node* APIs in BaseLib compare the *full* list
length against the PCD.

This turns the time complexity of node-level APIs from constant to linear,
and that of full-list manipulations from linear to quadratic.

As an example, consider the EFI_SHELL_FILE_INFO list, which is a data
structure that's widely used in the UEFI shell. I randomly extracted 5000
files from "/usr/include" on my laptop, spanning 1095 subdirectories out
of 1538, and then ran "DIR -R" in the UEFI shell on this tree. These are
the wall-clock times:

           PcdMaximumLinkedListLength  PcdMaximumLinkedListLength
           =1,000,000                  =0
           --------------------------  ---------------------------
FAT        4 min 31 s                        18 s
virtio-fs  5 min 13 s                  1 min 33 s

Checking list lengths against an arbitrary maximum (default: 1,000,000)
seems useless even in NOOPT and DEBUG builds, while the cost is
significant; so set the PCD to 0.

Cc: Anthony Perard <anthony.perard at citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
Cc: Jordan Justen <jordan.l.justen at intel.com>
Cc: Julien Grall <julien at xen.org>
Cc: Leif Lindholm <leif at nuviainc.com>
Cc: Peter Grehan <grehan at freebsd.org>
Cc: Philippe Mathieu-Daudé <philmd at redhat.com>
Cc: Rebecca Cran <rebecca at bsdio.com>
Cc: Sami Mujawar <sami.mujawar at arm.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3152
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 OvmfPkg/AmdSev/AmdSevX64.dsc | 1 +
 OvmfPkg/Bhyve/BhyveX64.dsc   | 1 +
 OvmfPkg/OvmfPkgIa32.dsc      | 1 +
 OvmfPkg/OvmfPkgIa32X64.dsc   | 1 +
 OvmfPkg/OvmfPkgX64.dsc       | 1 +
 OvmfPkg/OvmfXen.dsc          | 1 +
 6 files changed, 6 insertions(+)

diff --git a/OvmfPkg/AmdSev/AmdSevX64.dsc b/OvmfPkg/AmdSev/AmdSevX64.dsc
index bb7697eb324b..c1b3d27885b0 100644
--- a/OvmfPkg/AmdSev/AmdSevX64.dsc
+++ b/OvmfPkg/AmdSev/AmdSevX64.dsc
@@ -437,6 +437,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
diff --git a/OvmfPkg/Bhyve/BhyveX64.dsc b/OvmfPkg/Bhyve/BhyveX64.dsc
index b93fe30ae4e0..acf8f17ade12 100644
--- a/OvmfPkg/Bhyve/BhyveX64.dsc
+++ b/OvmfPkg/Bhyve/BhyveX64.dsc
@@ -429,6 +429,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index cd0acf021459..7cce8944e496 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -476,6 +476,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
 !endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 3bf493bdb08f..8d21dc0ed7b6 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -480,6 +480,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
 !endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index cebdbc9faabe..103af2fea7a5 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -480,6 +480,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
 !endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
index 12b7a87ee877..c15835d9d23c 100644
--- a/OvmfPkg/OvmfXen.dsc
+++ b/OvmfPkg/OvmfXen.dsc
@@ -356,6 +356,7 @@ [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxAuthVariableSize|0x2800
-- 
2.19.1.3.g30247aa5d201




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