linux-kernel - RE: [PATCH v4] cpuidle: Init cpuidle only for present CPUs

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Message-ID:
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Date: Fri, 7 Mar 2025 10:02:14 +0000
From: Jacky Bai <ping.bai@....com>
To: Sudeep Holla <sudeep.holla@....com>
CC: "rafael@...nel.org" <rafael@...nel.org>, "daniel.lezcano@...aro.org"
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Subject: RE: [PATCH v4] cpuidle: Init cpuidle only for present CPUs

Hi Sudeep,

> Subject: Re: [PATCH v4] cpuidle: Init cpuidle only for present CPUs
> 
> On Fri, Mar 07, 2025 at 04:03:03PM +0800, Jacky Bai wrote:
> > for_each_possible_cpu() is currently used to initialize cpuidle in
> > below cpuidle drivers:
> >   drivers/cpuidle/cpuidle-arm.c
> >   drivers/cpuidle/cpuidle-big_little.c
> >   drivers/cpuidle/cpuidle-psci.c
> >   drivers/cpuidle/cpuidle-riscv-sbi.c
> >
> > However, in cpu_dev_register_generic(), for_each_present_cpu() is used
> > to register CPU devices which means the CPU devices are only
> > registered for present CPUs and not all possible CPUs.
> >
> > With nosmp or maxcpus=0, only the boot CPU is present, lead to the
> > failure:
> >
> >   |  Failed to register cpuidle device for cpu1
> >
> > Then rollback to cancel all CPUs' cpuidle registration.
> >
> > Change for_each_possible_cpu() to for_each_present_cpu() in the above
> > cpuidle drivers to ensure it only registers cpuidle devices for CPUs
> > that are actually present.
> >
> > Fixes: b0c69e1214bc ("drivers: base: Use present CPUs in
> > GENERIC_CPU_DEVICES")
> > Reviewed-by: Dhruva Gole <d-gole@...com>
> > Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> > Tested-by: Yuanjie Yang <quic_yuanjiey@...cinc.com>
> > Signed-off-by: Jacky Bai <ping.bai@....com>
> > ---
> >  - v4 changes:
> >   - add changes for other cpuidle driver that has the similar issue
> >     as cpuidle-pcsi driver.
> >
> >  - v3 changes:
> >   - improve the changelog as suggested by Sudeep
> > ---
> >  drivers/cpuidle/cpuidle-arm.c        | 8 ++++----
> >  drivers/cpuidle/cpuidle-big_little.c | 2 +-
> >  drivers/cpuidle/cpuidle-psci.c       | 4 ++--
> >  drivers/cpuidle/cpuidle-riscv-sbi.c  | 4 ++--
> 
> 
> Why have you spared drivers/cpuidle/cpuidle-qcom-spm.c ? IIUC the issue
> exists there as well.
> 

For qcom-spm driver, it has below code logic to handle no cpu device case, and
no rollback to cancel the whole cpuidle registration. So I just leave it as it is.
Do we need to update it?

for_each_possible_cpu(cpu) {
        ret = spm_cpuidle_register(&pdev->dev, cpu);
        if (ret && ret != -ENODEV) {
                dev_err(&pdev->dev,
                        "Cannot register for CPU%d: %d\n", cpu, ret);
        }
}

BR
Jacky Bai
> --
> Regards,
> Sudeep