On 5/22/19 3:54 PM, Linus Torvalds wrote: > On Wed, May 22, 2019 at 8:40 AM Waiman Long <[email protected]> wrote: >> +#if defined(CONFIG_PREEMPT) && \ >> + (defined(CONFIG_DEBUG_PREEMPT) || !defined(CONFIG_X86)) >> +#define lockevent_percpu_inc(x) this_cpu_inc(x) >> +#define lockevent_percpu_add(x, v) this_cpu_add(x, v) > Why that CONFIG_X86 special case? > > On x86, the regular non-underscore versionm is perfectly fine, and the > underscore is no faster or simpler.
The condition is to use non-underscore version only when 1) It is a preempt kernel; AND 2) It either have CONFIG_DEBUG_PREEMPT on, OR it is a non-x86 system. > So just make it be > > #if defined(CONFIG_PREEMPT) > .. non-underscore versions.. > #else > .. underscore versions .. > #endif > > and realize that x86 simply doesn't _care_. On x86, it will be one > single instruction regardless. > > Non-x86 may prefer the underscore versions for the non-preempt case. I was thinking of doing that originally, but then change it so x86 preempt kernel will also use the underscore version as long as CONFIG_DEBUG_PREEMPT is not set. I can change it back if that makes it less confusing. Cheers, Longman
