55e0bf49a0
Probing for misaligned access speed takes about 0.06 seconds. On a system with 64 cores, doing this in smp_callin() means it's done serially, extending boot time by 3.8 seconds. That's a lot of boot time. Instead of measuring each CPU serially, let's do the measurements on all CPUs in parallel. If we disable preemption on all CPUs, the jiffies stop ticking, so we can do this in stages of 1) everybody except core 0, then 2) core 0. The allocations are all done outside of on_each_cpu() to avoid calling alloc_pages() with interrupts disabled. For hotplugged CPUs that come in after the boot time measurement, register CPU hotplug callbacks, and do the measurement there. Interrupts are enabled in those callbacks, so they're fine to do alloc_pages() in. Reported-by: Jisheng Zhang <jszhang@kernel.org> Closes: https://lore.kernel.org/all/mhng-9359993d-6872-4134-83ce-c97debe1cf9a@palmer-ri-x1c9/T/#mae9b8f40016f9df428829d33360144dc5026bcbf Fixes: 584ea6564bca ("RISC-V: Probe for unaligned access speed") Signed-off-by: Evan Green <evan@rivosinc.com> Link: https://lore.kernel.org/r/20231106225855.3121724-1-evan@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>