Re: [PATCH v2 10/10] ArmVirtPkg: disable list length checks in NOOPT and DEBUG builds

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 1/13/21 9:54 AM, Laszlo Ersek wrote:
> 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>
> ---
> 
> Notes:
>     v2:
>     - no changes
>     - pick up Ard's A-b
> 
>  ArmVirtPkg/ArmVirt.dsc.inc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>