linux-kernel - Re: [PATCH 1/2] perf/x86/rapl: Move the pmu allocation out of CPU hotplug

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Message-ID: <3b65fd68-8f5b-4029-8dbd-46c0b2cc34c7@linux.intel.com>
Date: Tue, 8 Oct 2024 16:10:27 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org,
 mingo@...hat.com, linux-kernel@...r.kernel.org
Cc: Oliver Sang <oliver.sang@...el.com>,
 Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
Subject: Re: [PATCH 1/2] perf/x86/rapl: Move the pmu allocation out of CPU
 hotplug



On 2024-10-08 12:33 p.m., Thomas Gleixner wrote:
> On Fri, Sep 13 2024 at 10:10, kan liang wrote:
>> +static void __init init_rapl_pmu(void)
>> +{
>> +	struct rapl_pmu *pmu;
>> +	s32 rapl_pmu_idx;
>> +	int cpu;
>> +
>> +	cpus_read_lock();
>> +
>> +	for_each_cpu(cpu, cpu_online_mask) {
> 
> How is that supposed to work, when not all CPUs are online when
> init_rapl_pmus() is invoked?
> 

RAPL is a module. The module_init() is called during do_initcalls(),
which is after the smp_init(). The cpu_online_mask has been setup in the
smp_init().

I also patched the kernel to double check. The cpu_online_mask indeed
shows all the online CPUs.

[    7.021212] smp: Brought up 1 node, 48 CPUs
[    7.021212] smpboot: Total of 48 processors activated (211200.00
BogoMIPS)
... ...
[   16.557323] RAPL PMU: rapl_pmu_init: cpu_online_mask 0xffffffffffff


Thanks,
Kan