linux-kernel - Re: [PATCH] MIPS: CPS: Optimise delay CPU calibration for SMP

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Message-Id: <105ed884-9ee8-429a-9937-d8f58a221faa@app.fastmail.com>
Date: Thu, 22 May 2025 14:03:49 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Gregory CLEMENT" <gregory.clement@...tlin.com>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>
Cc: "Vladimir Kondratiev" <vladimir.kondratiev@...ileye.com>,
 Théo Lebrun <theo.lebrun@...tlin.com>,
 "Tawfik Bayouk" <tawfik.bayouk@...ileye.com>,
 "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: CPS: Optimise delay CPU calibration for SMP



在2025年5月21日周三 上午8:47，Gregory CLEMENT写道：
> Hello Jiaxun,
>
>> 在2025年5月20日周二 下午4:21，Gregory CLEMENT写道：
>> [...]
>>>
>>> This allows to implement calibrate_delay_is_known(), which will return
>>> 0 (triggering calibration) only for the primary CPU of each
>>> cluster. For other CPUs, we can simply reuse the value from their
>>> cluster's primary CPU core.
>>
>> Is __cpu_primary_cluster_mask really necessary?
>>
>> Maybe we can just test if current CPU is the first powered up CPU
>> in the cluster?
>
> That is exactly the point of __cpu_primary_cluster_mask: setting in an
> efficient way the first powered-up CPU for each cluster. This adds only
> a single variable (which is actually just a long) and allows for minimal
> impact during boot time, by doing the minimum write and read operations
>
> I don't see a better alternative. What do you have in mind ?

Maybe we can try mips_cps_first_online_in_cluster()?

[...]

Thanks

-- 
- Jiaxun