Hi Greg, On 2018/10/13 15:04, Greg Kroah-Hartman wrote: > On Sat, Oct 13, 2018 at 02:47:29PM +0800, Gao Xiang wrote: >> It is better to use smp_cond_load_relaxed instead >> of busy waiting for bit_spinlock. > > Why? I think we need some kind of "proof" that this is true before > being able to accept a patch like this, don't you agree?
There are some materials which discuss smp_cond_load_* earlier. https://patchwork.kernel.org/patch/10335991/ https://patchwork.kernel.org/patch/10325057/ In ARM64, they implements a function called "cmpwait", which uses hardware instructions to monitor a value change, I think it is more energy efficient than just do a open-code busy loop... And it seem smp_cond_load_* is already used in the current kernel, such as: ./kernel/locking/mcs_spinlock.h ./kernel/locking/qspinlock.c ./kernel/sched/core.c ./kernel/smp.c For other architectures like x86/arm64, I think they could implement smp_cond_load_* later. Thanks, Gao Xiang > > thanks, > > greg k-h >
