On 5/23/19 10:58 AM, Will Deacon wrote: > On Wed, May 22, 2019 at 12:54:13PM -0700, 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. >> >> 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. > To be honest, given this depends on LOCK_EVENT_COUNTS, I'd be inclined to > keep things simple and drop the underscore versions entirely. Saves having > to worry about things like "could I take an interrupt during the add?". > I have sent out the v2 patch that simplifies the condition. Now the underscore versions will be used for !preempt kernel and non-underscore version used in preempt kernel. The non-underscore versions may generate a lot more unnecessary code when CONFIG_PREEMPT_COUNT is defined.
Cheers, Longman
