netdev - Re: [PATCH net-next v4 3/9] dpll: core: Add DPLL framework base functions

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Date: Tue, 15 Aug 2023 19:38:41 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jiri Pirko <jiri@...nulli.us>,
 Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
 Jonathan Lemon <jonathan.lemon@...il.com>, Paolo Abeni <pabeni@...hat.com>,
 Milena Olech <milena.olech@...el.com>,
 Michal Michalik <michal.michalik@...el.com>,
 linux-arm-kernel@...ts.infradead.org, poros@...hat.com, mschmidt@...hat.com,
 netdev@...r.kernel.org, linux-clk@...r.kernel.org,
 Bart Van Assche <bvanassche@....org>, intel-wired-lan@...ts.osuosl.org,
 Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v4 3/9] dpll: core: Add DPLL framework base
 functions

On 15/08/2023 19:28, Jakub Kicinski wrote:
> On Tue, 15 Aug 2023 19:20:31 +0100 Vadim Fedorenko wrote:
>>>> +	ret = xa_alloc(&dpll_device_xa, &dpll->id, dpll, xa_limit_16b,
>>>> +		       GFP_KERNEL);
>>>
>>> Why only 16b and why not _cyclic?
>>
>> I cannot image systems with more than 65k of DPLL devices. We don't
>> store any id's of last used DPLL device, so there is no easy way to
>> restart the search from the last point. And it's not a hot path to
>> optimize it.
> 
> I think this gets used under the xa_lock() so you can just add a static
> variable inside the function to remember previous allocation.
> 
> I don't expect >64k devices either, obviously, but what are we saving
> by not allowing the full u32 range?

I don't see any benefits for either _cyclic or u32 range, but if you 
insist I can change it.