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From: Catalin Marinas on 25 Jun 2010 13:20
On Tue, 2010-06-15 at 13:46 +0100, Phil Carmody wrote:
> With several sections per module, and dozens of modules, the
> searches down the linked list would dominate the lookup time,
> dwarfing any savings from the binary search within the section.
>
> A simple move-to-front optimisation exploits the commonality
> of the code paths taken, and in simple real-world tests reduces
> the number of steps in the search to barely more than 1.
>
> Signed-off-by: Phil Carmody <ext-phil.2.carmody(a)nokia.com>
> ---
> arch/arm/kernel/unwind.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index dd81a91..2e88abf 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -146,6 +146,8 @@ static struct unwind_idx *unwind_find_idx(unsigned long addr)
> addr < table->end_addr) {
> idx = search_index(addr, table->start,
> table->stop - 1);
> + /* MTF with 50 modules: 80 steps becomes ~1 */
> + list_move(&table->list, &unwind_tables);

That's a good optimisation. Could you please expand the "MTF" comment in
the code a bit more? Otherwise,

Acked-by: Catalin Marinas <catalin.marinas(a)arm.com>

--
Catalin

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