On Sun, 2 Oct 2011 21:57:07 +0800
Wei Yang <weiyang.kernel@xxxxxxxxx> wrote:
> Dear experts,
>
> I am viewing the source code of __release_region() in kernel/resource.c.
> And I have one comment for the performance issue.
>
> For example, we have a resource tree like this.
> 10-89
> 20-79
> 30-49
> 55-59
> 60-64
> 65-69
> 80-89
> 100-279
>
> If the caller wants to release a region of [50,59], the original code will
> execute four times in the for loop in the subtree of 20-79.
>
> After changing the code below, it will execute two times instead.
>
> By using the "git annotate", I see this code is committed by Linus as the
> initial version. So don't get more information about why this code is
> written
> in this way.
>
> Maybe the case I thought will not happen in the real world?
>
> Your comment is warmly welcome. :)
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 8461aea..81525b4 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -931,7 +931,7 @@ void __release_region(struct resource *parent,
> resource_size_t start,
> for (;;) {
> struct resource *res = *p;
>
> - if (!res)
> + if (!res || res->start > start)
Hmm ?
res->start > end ?
Thanks,
-Kame
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