Re: [PATCH 2/3] memblock: Make finding index faster when modify regions.

[Peng Zhang]

在 2023/1/16 15:37, Mike Rapoport 写道:
> On Mon, Jan 16, 2023 at 11:17:40AM +0800, Peng Zhang wrote:
> > 在 2023/1/15 22:02, Mike Rapoport 写道:
> > > Hi,
> > >
> > > On Fri, Jan 13, 2023 at 04:26:58PM +0800, Peng Zhang wrote:
> > > > We can use binary search to find the index to modify regions in
> > > > memblock_add_range() and memblock_isolate_range(). Because the
> > > > arrangement of regions is ordered. It may be faster when there are
> > > > many regions. So implemented a binary search and a new macro to walk
> > > > regions.
> > >
> > > Did you see a measurable speedup with this optimization?
> > > I'm not in favor of micro-optimizations that complicate code.
> > Thank you for your reply. I haven't measured this patch yet, theoretically
> > this small optimization might be difficult to observe.
> > If you think this patch complicates the code, you can ignore this patch.
> >
> > These three patches are independent and they can be applied independently.
> > The logic of the third patch is very simple. It will not complicate the
> > code. It is tested by the default configuration of qemu. The total number of
> > iterations of memblock_merge_regions() in the third patch is reduced from
> > more than one thousand to more than one hundred, this is only in the case of
> > a small number of regions. Can you consider the third patch?
>
> Can you please send the numbers and show how did you obtained them?
>
> > Sincerely yours,
> > Peng.
I obtained the numbers like this:

void memblock_merge_regions(struct memblock_type *type) {
	static int iteration_count = 0;
	static int max_nr_regions = 0;

	max_nr_regions = max(max_nr_regions, (int)type->cnt);
	...
	while () {
		iteration_count++;
		...
	}
	pr_info("iteration_count: %d max_nr_regions %d", iteration_count, 
max_nr_regions);
}

Boot the kernel by qemu.
The folowing numbers is the last output.

master branch:
iteration_count: 1762 max_nr_regions 41

patched:
iteration_count: 182 max_nr_regions 41

If max_nr_regions is larger, the difference will be more.

Thanks.

Sincerely yours,
Peng