Messages in this thread | | | Date | Wed, 27 Nov 2019 17:44:02 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH] cpufreq: vexpress-spc: Fix wrong alternation of policy->related_cpus during CPU hp |
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On 27-11-19, 12:08, Sudeep Holla wrote: > On Wed, Nov 27, 2019 at 12:48:01PM +0100, Dietmar Eggemann wrote: > > Since commit ca74b316df96 ("arm: Use common cpu_topology structure and > > functions.") the core cpumask has to be modified during cpu hotplug > > operations. > > > > ("arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC") > > [1] fixed that but revealed another issue on TC2, i.e in its cpufreq > > driver. > > > > During CPU hp stress operations on multiple CPUs, policy->related_cpus > > can be altered. This is wrong since this cpumask should contain the > > online and offline CPUs. > > > > The WARN_ON(!cpumask_test_cpu(cpu, policy->related_cpus)) in > > cpufreq_online() triggers in this case. > > > > The core cpumask can't be used to set the policy->cpus in > > ve_spc_cpufreq_init() anymore in case it is called via > > cpuhp_cpufreq_online()->cpufreq_online()->cpufreq_driver->init(). > > > > An empty online() callback can be used to avoid that the init() > > driver function is called during CPU hotplug in so that > > policy->related_cpus will not be changed. > > > > Unlike DT based drivers, it not easy to get the fixed cpumask unless we > add some mechanism to extract it based on clks/OPP added. I prefer > this simple solution instead.
I will call this a work-around for the problem and not really the solution, though I won't necessarily oppose it. There are cases which will break even with this solution.
- Boot board with cpufreq driver as module. - Offline all CPUs except CPU0. - insert cpufreq driver. - online all CPUs.
Now there is no guarantee that the last online will get the mask properly, if I have understood the problem well :)
But yeah, who does this kind of messy work anyway :)
FWIW, we need a proper way (may be from architecture code) to find list of all CPUs that share clock line.
-- viresh
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