Re: [PATCH v2 0/4] cpumask: improve on cpumask_local_spread() locality

Tariq Toukan
2022-11-28T06:39:34Z

On 11/17/2022 2:23 PM, Valentin Schneider wrote:
> On 15/11/22 10:32, Yury Norov wrote:
>> On Tue, Nov 15, 2022 at 05:24:56PM +0000, Valentin Schneider wrote:
>>>
>>> Is this meant as a replacement for [1]?
>>
>> No. Your series adds an iterator, and in my experience the code that
>> uses iterators of that sort is almost always better and easier to
>> understand than cpumask_nth() or cpumask_next()-like users.
>>
>> My series has the only advantage that it allows keep existing codebase
>> untouched.
>>
>
> Right
>
>>> I like that this is changing an existing interface so that all current
>>> users directly benefit from the change. Now, about half of the users of
>>> cpumask_local_spread() use it in a loop with incremental @i parameter,
>>> which makes the repeated bsearch a bit of a shame, but then I'm tempted to
>>> say the first point makes it worth it.
>>>
>>> [1]: https://lore.kernel.org/all/20221028164959.1367250-1-vschneid@redhat.com/
>>
>> In terms of very common case of sequential invocation of local_spread()
>> for cpus from 0 to nr_cpu_ids, the complexity of my approach is n * log n,
>> and your approach is amortized O(n), which is better. Not a big deal _now_,
>> as you mentioned in the other email. But we never know how things will
>> evolve, right?
>>
>> So, I would take both and maybe in comment to cpumask_local_spread()
>> mention that there's a better alternative for those who call the
>> function for all CPUs incrementally.
>>
>
> Ack, sounds good.
>

Good.
Is a respin needed, to add the comment mentioned above?