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Message-ID: <665b6081-be55-de9a-1f7f-70a143df329d@gmail.com>
Date: Mon, 28 Nov 2022 08:39:24 +0200
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Valentin Schneider <vschneid@...hat.com>,
Yury Norov <yury.norov@...il.com>
Cc: linux-kernel@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Barry Song <baohua@...nel.org>,
Ben Segall <bsegall@...gle.com>,
haniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Gal Pressman <gal@...dia.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Heiko Carstens <hca@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Jakub Kicinski <kuba@...nel.org>,
Jason Gunthorpe <jgg@...dia.com>,
Jesse Brandeburg <jesse.brandeburg@...el.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Juri Lelli <juri.lelli@...hat.com>,
Leon Romanovsky <leonro@...dia.com>,
Mel Gorman <mgorman@...e.de>,
Peter Zijlstra <peterz@...radead.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Saeed Mahameed <saeedm@...dia.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tariq Toukan <tariqt@...dia.com>,
Tony Luck <tony.luck@...el.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
linux-rdma@...r.kernel.org
Subject: Re: [PATCH v2 0/4] cpumask: improve on cpumask_local_spread()
locality
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?
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