From: Laszlo Ersek <lersek@redhat.com>
Date: Wed, 13 Jan 2021 08:54:53 +0000 (+0100)
Subject: ArmVirtPkg: disable list length checks in NOOPT and DEBUG builds
X-Git-Tag: edk2-stable202102~127
X-Git-Url: https://git.proxmox.com/?p=mirror_edk2.git;a=commitdiff_plain;h=6e5586863148773c15399ead249711143a74d2d0

ArmVirtPkg: disable list length checks in NOOPT and DEBUG builds

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@arm.com>
Cc: Julien Grall <julien@xen.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3152
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Message-Id: <20210113085453.10168-11-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---

diff --git a/ArmVirtPkg/ArmVirt.dsc.inc b/ArmVirtPkg/ArmVirt.dsc.inc
index 9ec9293047..d9abadbe70 100644
--- a/ArmVirtPkg/ArmVirt.dsc.inc
+++ b/ArmVirtPkg/ArmVirt.dsc.inc
@@ -290,7 +290,7 @@
 [PcdsFixedAtBuild.common]
   gEfiMdePkgTokenSpaceGuid.PcdMaximumUnicodeStringLength|1000000
   gEfiMdePkgTokenSpaceGuid.PcdMaximumAsciiStringLength|1000000
-  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|1000000
+  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength|0
   gEfiMdePkgTokenSpaceGuid.PcdSpinLockTimeout|10000000
   gEfiMdePkgTokenSpaceGuid.PcdUefiLibMaxPrintBufferSize|320