On 07.08.2024 13:29, oleksii.kuroc...@gmail.com wrote: > On Tue, 2024-07-30 at 11:17 +0200, Jan Beulich wrote: >>>>> + >>>>> +static void sbi_cpumask_to_hartmask(const struct cpumask >>>>> *cmask, >>>>> + struct cpumask *hmask) >>>> >>>> I doubt it is valud to re-use struct cpumask for hart maps. >>> Why not? Would it be better to use unsigned long *hmask? >> >> It's not only better, but imo a requirement. Unless there's a >> guarantee >> by the spec that hart IDs for any subset of harts are sequential and >> starting from 0, you just can't assume they fall in the [0,NR_CPUS) >> or >> really [0,nr_cpu_ids) range. Yet without that you simply can't >> (ab)use >> struct cpumask (and btw it wants to be cpumask_t everywhere). >> >> You may want to take a look at struct physid_mask that we have on x86 >> for the equivalent purpose. > Could you please explain me why factor 4 is used in defintion of > MAX_APICS and why 256 ( is it a maximum number of APIC IDs can be > supported in the system? ): > #define MAX_APICS MAX(256, 4 * NR_CPUS)
Both numbers are pretty arbitrary, I suppose. APIC IDs need not be contiguous, which is what the multiplication by 4 is trying to cover for. Plus on old (non-x2APIC) systems APIC IDs are only 8 bits wide, and allowing for all possible values in that case is cheap enough - hence the 256. Jan
