[edk2-devel] [PATCH v2 10/10] ArmVirtPkg: 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.

(See some example OVMF numbers in the previous patch.)

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

Cc: Ard Biesheuvel <ard.biesheuvel at arm.com>
Cc: Julien Grall <julien at xen.org>
Cc: Leif Lindholm <leif at nuviainc.com>
Cc: Philippe Mathieu-Daudé <philmd at redhat.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>
Acked-by: Ard Biesheuvel <ard.biesheuvel at arm.com>
---

Notes:
    v2:
    - no changes
    - pick up Ard's A-b

 ArmVirtPkg/ArmVirt.dsc.inc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ArmVirtPkg/ArmVirt.dsc.inc b/ArmVirtPkg/ArmVirt.dsc.inc
index 9ec92930472d..d9abadbe708c 100644
--- a/ArmVirtPkg/ArmVirt.dsc.inc
+++ b/ArmVirtPkg/ArmVirt.dsc.inc
@@ -290,7 +290,7 @@ [PcdsFeatureFlag.AARCH64]
 [PcdsFixedAtBuild.common]
   gEfiMdePkgTokenSpaceGuid.PcdMaximumUnicodeStringLength|1000000
   gEfiMdePkgTokenSpaceGuid.PcdMaximumAsciiStringLength|1000000
-  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|1000000
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
   gEfiMdePkgTokenSpaceGuid.PcdSpinLockTimeout|10000000
   gEfiMdePkgTokenSpaceGuid.PcdUefiLibMaxPrintBufferSize|320
 
-- 
2.19.1.3.g30247aa5d201



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