Messages in this thread | | | Subject | Re: [PATCH] cpufreq: vexpress-spc: Fix wrong alternation of policy->related_cpus during CPU hp | From | Dietmar Eggemann <> | Date | Wed, 27 Nov 2019 15:58:49 +0100 |
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On 27/11/2019 14:32, Sudeep Holla wrote: > On Wed, Nov 27, 2019 at 05:44:02PM +0530, Viresh Kumar wrote: >> On 27-11-19, 12:08, Sudeep Holla wrote: >>> On Wed, Nov 27, 2019 at 12:48:01PM +0100, Dietmar Eggemann wrote:
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>>> 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. >> > > I agree and that's the reason I spoke out my thought aloud here :) > >> - Boot board with cpufreq driver as module. >> - Offline all CPUs except CPU0. >> - insert cpufreq driver. >> - online all CPUs. >> > > Indeed, not just boot anytime since it's a module :) > >> Now there is no guarantee that the last online will get the mask >> properly, if I have understood the problem well :) >> > > Yes > >> But yeah, who does this kind of messy work anyway :) >> > > I won't bet on that ;) > >> FWIW, we need a proper way (may be from architecture code) to find >> list of all CPUs that share clock line. >> > > Yes but there's no architectural way. I need to revise and see tc2_pm.c > to check if we can do any magic there.
I'm fine with finding a better solution to return a fixed topology core cpumask or calling this patch a workaround. AFAICS, only TC2 is affected.
("arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC") is needed for other systems as well in case we have commit ca74b316df96 ("arm: Use common cpu_topology structure and functions."). We probably don't want to revert commit ca74b316df96?
We do CPU hp stress tests in our EAS mainline integration test suite https://developer.arm.com/tools-and-software/open-source-software/linux-kernel/energy-aware-scheduling/eas-mainline-development and there is where we initially encountered this issue on TC2.
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