On Wed, Oct 21, 2020 at 05:07:30PM +0100, Qais Yousef wrote: > On 10/21/20 16:23, Will Deacon wrote: > > > > If a cpumask is easier to implement and easier to use, then I think that's > > > > what we should do. It's also then dead easy to disable if necessary by > > > > just returning 0. The only alternative I would prefer is not having to > > > > expose this information altogether, but I'm not sure that figuring this > > > > out from MIDR/REVIDR alone is reliable. > > > > > > I did suggest this before, but I'll try gain. If we want to assume a custom > > > bootloader and custom user space, we can make them provide the mask. > > > > Who mentioned a custom bootloader? In the context of Android, we're > > Custom bootloader as in a bootloader that needs to opt-in to enable the > feature (pass the right cmdline param). Catalin suggested to make this a sysctl > to allow also for runtime toggling. But the initial intention was to have this > to enable it at cmdline. Hmm, ok, I don't think allowing the cmdline to be specified means its a custom bootloader. > > talking about a user-space that already manages scheduling affinity. > > > > > For example, the new sysctl_enable_asym_32bit could be a cpumask instead of > > > a bool as it currently is. Or we can make it a cmdline parameter too. > > > In both cases some admin (bootloader or init process) has to ensure to fill it > > > correctly for the target platform. The bootloader should be able to read the > > > registers to figure out the mask. So more weight to make it a cmdline param. > > > > I think this is adding complexity for the sake of it. I'm much more in > > I actually think it reduces complexity. No special ABI to generate the mask > from the kernel. The same opt-in flag is the cpumask too. Maybe I'm misunderstanding your proposal but having a cpumask instead of a bool means you now have to consider policy on a per-cpu basis, which adds an extra dimension to this. For example, do you allow that mask to be changed at runtime so that differents sets of CPUs now support 32-bit? Do you preserve it across hotplug? Will
