Re: [PATCH] topology: make for_each_node_with_cpus() O(N)

[Yury Norov <yury.norov@gmail.com>]

On Fri, May 09, 2025 at 07:04:15PM +0200, Andrea Righi wrote:
> Hi Yury,
> 
> On Fri, May 09, 2025 at 12:20:08PM -0400, Yury Norov wrote:
> > From: Yury Norov [NVIDIA] <yury.norov@gmail.com>
> > 
> > for_each_node_with_cpus() calls nr_cpus_node() at every iteration, which
> > makes it O(N^2). Kernel tracks such nodes with N_CPU record in node_states
> > array. Switching to it makes for_each_node_with_cpus() O(N).
> 
> Makes sense to me.
> 
> Maybe we should mention that previously we were only considering online
> nodes with CPUs assigned. Now, we can include also offline nodes with CPUs
> assigned (assuming it's possible)?
> 
> Semantically speaking, since the name doesn't include "online", it seems
> more logical to ignore the state of the node. And if checking the online
> state is required, the user can just use node_online() within the loop.

OK. I'll take your comment and move the patch with bitmap-for-next, if
no objections.

Thanks,
Yury