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| author | Laszlo Ersek <lersek@redhat.com> | 2021-01-13 09:54:52 +0100 |
|---|---|---|
| committer | mergify[bot] <37929162+mergify[bot]@users.noreply.github.com> | 2021-01-19 18:23:28 +0000 |
| commit | d3f3c942013a6f1c6bde7ba6ca41ca97bab51663 (patch) | |
| tree | d62f751ee82f1d7336fc8130bc066fa14390abcb /OvmfPkg/OvmfPkgIa32X64.dsc | |
| parent | c8ce60eb2938c7194b317480de7f3d645aecdf6e (diff) | |
| download | edk2-d3f3c942013a6f1c6bde7ba6ca41ca97bab51663.tar.gz edk2-d3f3c942013a6f1c6bde7ba6ca41ca97bab51663.tar.bz2 edk2-d3f3c942013a6f1c6bde7ba6ca41ca97bab51663.zip | |
OvmfPkg: 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.
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@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Peter Grehan <grehan@freebsd.org>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rebecca Cran <rebecca@bsdio.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: <20210113085453.10168-10-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Diffstat (limited to 'OvmfPkg/OvmfPkgIa32X64.dsc')
| -rw-r--r-- | OvmfPkg/OvmfPkgIa32X64.dsc | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc index 4d7a26636a..3bfec9196e 100644 --- a/OvmfPkg/OvmfPkgIa32X64.dsc +++ b/OvmfPkg/OvmfPkgIa32X64.dsc @@ -482,6 +482,7 @@ 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
|