On 10/22/20 09:16, Catalin Marinas wrote: > On Wed, Oct 21, 2020 at 09:26:27PM +0100, Will Deacon wrote: > > On Wed, Oct 21, 2020 at 08:57:36PM +0100, Qais Yousef wrote: > > > On 10/21/20 18:23, Will Deacon wrote: > > > > On Wed, Oct 21, 2020 at 05:07:30PM +0100, Qais Yousef wrote: > > > > > > > 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 > > > > > > What I meant is that if we change the requirement to opt-in from a boolean > > > switch > > > > > > sysctl.enable_32bit_asym=1 > > > > > > to require the bootloader/init scripts provide the mask of aarch32 capable cpus > > > > > > sysctl.asym_32bit_cpus=0xf0 > [...] > > > * We don't need a separate API to export which cpus are 32bit capable. > > > They can read it directly from /proc/sys/kernel/asym_32bit_cpus. > > > When it's 0 it means the system is not asymmetric. > > > > I don't see how this is better than a separate cpumask for this purpose. > > It feels like you're trying to overload the control and the identification, > > but that just makes things confusing and hard to use as I now need to know > > which logical CPUs correspond to which physical CPUs in order to set the > > command-line. I tend to disagree with some of the statements. But I'll leave it at that. Whatever makes the ship move :) > I agree. Let's leave the identification to the kernel as it has access > to the CPUID registers and can provide the cpumask. The control in this > case doesn't need to be more than a boolean and its meaning is that the > user knows what it is doing. Thanks -- Qais Yousef
